



















































































































































































































































































PARKER’S 


NATURAL AND EXPERT AI ENT AI 











































































































































-1 


SCHOOL COMPENDIUM 

OP 

NATURAL AND EXPERIMENTAI 

PHILOSOPHY, 

EMB RACING THE ELEMENTARY PRINCIPLES OP 


MECHANICS, HYDROSTATICS, HYDRAULICS. PNEUMATICS, ACOUSTICS, PYRONOMICS. 
OPTICS, ELECTRICITY, GALVANISM, MAGNETISM. ELECTRO MAGNETISM, 
MAGNETO-ELECTRICITY, AND ASTRONOMY 

« 

CONTAINING ALSO A DESCKIPTION DF THE 


STEAM AND LOCOMOTIVE ENGINES, 

AND OF THE 


ELECTRO-MAGNETIC TELEGRAPH 

BY 

RICHARD GREEN PARKER, A. M., 

it 

LATH PRINCIPAL OF THE JOHNSON GRAMMAR 8CHOOL, BOSTON ; AUTHOR OF “ AIDS TO 
ENGLISH COMPOSITION,” A SERIES OF “SCHOOL READERS,” 
GEOGRAPHICAL QUESTIONS,” ETC., ETO. 


Delectando pariter qne monendo. 
Prodesse quam conspict 


COllRECTEP, ENLARGED AND IMPROVED. 


NEVY YORK: 

COLLINS & BROTHER, PUBLISHERS, 

106 LEONARD STREET. 

18 ( 0 . 







QC .12 
. 9 - 2.1 

TEXT BOOKS IN NATURAL SCIENCE, 

COLLINS & BROTHER, PUBLISHERS, 


PARKER’S SERIES. 

Parker’s Philosophy, Part I.; or, Philosophy in Familial 
Conversations. Designed to teach young children to think. By 
Richard Green Parker, A.M. 150 pp. 18mo. 

Parker’s Philosophy, Part II.; or, First Lessons in Na- 
tural Philosophy. Designed to teach the elements of the science 
By R. G. Parker, A.M. 150 pp. 16mo. 

Parker’s Philosophy, Part III. A compendium of Naturai 
and Experimental Philosophy, embracing the Elementary Principles 
of Mechanics, Hydrostatics, Hydraulics, Acoustics, Pneumatics, 
Pyronomics, Optics, Electricity, Galvanism, Magnetism, Electro- 
Magnetism, Magneto-Electricity, and Astronomy. Containing also 
a description of the Steam and Locomotive Engines, and of the 
Electro-Magnetic Telegraph. A new edition, corrected, enlarged, and 
improved. By R. G. Parker, AM. 470 pp. 12mo. 

OLMSTED’S SERIES. 

Snell’s Olmsted’s College Philosophy. An introduc- 

Hon to Natural Philosophy for college students. Py Professor Denison 
Olmhtead, LL.D., Yale College. A new edition, revised and re-written. 
By Professor E. Snell, Amherst College. 500 pp. 8vo. 

Olmsted’s Rudiments. Rudiments of Natural Philosophy 
and Astronomy for Younger Classes. By Professor Olmsted. Re 
vised and improved edition. Large 18 mo. 

Olmsted’s School Astronomy. A compendium of As¬ 
tronomy, containing the elements of the science familiarly explained 
and illustrated, with the latest discoveries, adapted to the use of 
schools and academies. By Professor Olmsted. 12 mo. 

* ’ * 

Olmsted’s College Astronomy. An Introduction to As¬ 
tronomy for College Students. By Professor Olmsted. 8vo. 


• Entered according to Act of Congress, in the year 1S53, 

By A. S. BARNES & CO., 

Tn the Clei k’s Office of the District Court of the United States for the Southern 
District of New York. 


^~lss-»Slx\' 2. i 

o 


• c i% 


n 




PREFACE. 


v in the year 1837, the school-committee of the city of Boston 
'iidered a lew articles of philosophical apparatus to be furnished 
for each of the grammar-schools of that city; and the author of this 
work, who for many years had been at the head of one of those 
schools, finding no elementary work, unencumbered with extraneous 
matter, suitable k) explain the apparatus, attempted to supply the 
deficiency, ^fhe result was the first edition of this work.^A few 
years afterwards, the philosophical apparatus was exchanged for 
one of better construction, and much more extended application, 
and an enterprising publishing house in New York induced tne 
author to revise and extend his work. This was done in the year 
1848. Since that time the progress of science has been so great 
that another revision is imperatively demanded; and the author, 
anxious not to be “behind the age” has made another careful 
revision, in which he is conscious of no omission in the notices of 
<he present state of science, in the departments embraced in this 
volume, suitable for a work designed to be strictly elementary, ana 
designed for those only whose progress in “ the exact sciences ' 
must necessarily be limited. The “ Questions ” which have ap¬ 
peared in previous editions he had no hand in preparing. Indeed, 
in his opinion, such appendages to school-books, in the hands of 
experienced teachers, are of very questionable expediency. But, 
as it is a custom most honored in “observance ” he has, in this 


l* 



VI 


PREFACE. 


edition of 1854, complied with that custom, and prepared them 
with his own hands. If he is not deceived in the result of his 
iaoors, his work will commend itself by the following features: 

1. It is adapted to the 'present state of natural science; em¬ 
braces a wider field, and contains a greater amount of information 
on the respective subjects of which it treats, than any other ele¬ 
mentary treatise of its size. 

2. It contains engravings of the Boston school set of philoso- 
vkical apparatus ; a description of the instruments, and an account 
of many experiments which can be performed by means of the 
apparatus. 

3. It is enriched by a representation and a description of the 
Locomotive and the Stationary Steam Engines , and the various 
forms of the Electric Telegraph now in operation in this country. 

4. The subjects of Pyronomics, Electricity, Magnetism, Electro- 
Magnetism, and Magneto-Electricity, as well as Astronomy, have 
large space allotted to them. Most of the latest discoveries in 
physical science have also received their due share of attention. 

5. It is peculiarly adapted to the convenience of study and of 
recitation, by the figures and diagrams being first placed side by 
side with the illustrations, and then repeated on separate leaves at 
the end of the volume. The number is also given, where each 
principle may be found to which allusion is made throughout the 
volume. Suitable questions, also prepared by the author himself, 
and obnoxious to no objection as “ leading questions have been 
placed in immediate connection with the most important principles 
contained in the volume. 

6. It presents the most important principles of science in a 
larger type; while the deductions from these principles, and the 
illustrations, are contained in a smaller letter. Much useful and 


PREFACE. 


Vl> 

ntc testing matter is also crowded into notes at the bottom of the 
page. By this arrangement, the pupil can never be at a loss tc 
distinguish the parts of a lesson which are of primary importance; 
nor will he be in danger of mistaking theory and conjecture for fact. 

7. It contains a number of original illustrations, which'the 
author has found more intelligible to young students than those 
with which he has met elsewhere. 

8. Nothing, has been omitted which is usually contained in an 
elementary treatise. 

A work of this kind, from its very nature, admits but little 
originality. The whole circle of the .sciences consists of principles 
deduced from the discoveries of different individuals, in different 
ages, thrown into common stock. The whole, then, is common 
property, and belongs exclusively to no one. The merit, there* 
fore, of an elementary treatise on natural science must rest solely 
on the judiciousness of its selections. In many of the works from 
which extracts have been taken for this volume, the author has 
found the same language and expressions without the usual 
marks of quotation. Being at a loss, therefore, whom to credit 
for some of the expressions which he has borrowed, he makes this 
general acknowledgment, in the hope that it may be said of him, 
as it was once said of the Mantuan bard, tl at “ he has adormd 
his thefts , and polished the diamonds tv kick he has stolen 


ADVERTISEMENT TO THE NEW EDITION. 


In the revision of this work the author has endeavored to present 
his materials under a better classification. The omission of seventy- 
five pages of Questions, prepared by another hand, found at the end 
of the book in previous editions, has given room for a large collec¬ 
tion of new facts and principles which the present improved state 
of science has revealed, without materially enlarging the size of the 
volume. The author now gives it to the world, in confidence that 
it is much more deserving of the unexpected favor it has received. 
All changes in a text-book are necessarily attended with inconve 
niences to teachers; but they who would keep pace with the pro¬ 
gress of science must submit to such inconvenience, or be behind 
the age. The present is emphatically the age of “ prepress” and 
they who profess to record the triumphs of science must keep a 
blank page in their journals for the record of new conquests. So 
much of apology seems to be due for the appearance of a new revi¬ 
sion of this volume so soon after the former revision. The author 
indulges the belief that no advance has been made in fact, in prin¬ 
ciple, or in physical law, which has not received its due share of 
attention so far as is consistent with the plan of a work professing 
<c be strictly slemont<*.iy. 



LIST OF WORKS 


WifiCH HAVE BREN CONSULTED, OR FROM WHICH EXTRACTS HAVE BESS 
TAKEN, IN THE PREPARATION OP THIS VOLUME. 


Annals of Philosophy; Arnott’s Elements of Physics ; Bartlett * 
Philosophy; Bigelow’s Technology ; Cambridge Physics ; Chambeis’ 
Dictionary; Enfield’s, Olmsted’s, Smith’s, Blair’s, Bakewell’s, Dra 
pcrs, Grund's, Johnson’s, Jones’, Comstock’s, and Conversations on. 
Natural Philosophy ; Davis’ Manual of Magnetism ; Encyclopedia 
Americana ; Franklin’s Philosophical Papers ; Henry’s Chemistry , 
King’s Manual 6f Electricity ; Lardner’s Works ; Library of Useful 
Knowledge ; Orbs of Heaven ; Paxton’s Introduction to the Study 
of Anatomy ; Pambour on Locomotive Engines on Railways ; Penny 
Cyclopedia ; Peschel’s Elements of Physics ; Philips’ Astronomy ; 
Sir John Herschel’s Astronomy ; Silliman’s Journal of Science ; 
Singer’s Electricity; Scientific Class Book; Scientific Dialogues ; 
Smith’s Explanatory Key ; The Year Book; Turner’s Chemistry ; 
Wilkins’ Astronomy ; Worcester’s and the American School Geog¬ 
raphy; Lathrop, Mclntire and Keith, on the Globes; World’s 
Progress; Annual of Scientific Discovery; Webster’s Dictionary; 
Treasury of Knowledge ; Gregory’s Chemistry; Science of Familiar 
Things; Loomis’ Elements of Geology; Chambers’ Educational 
Course; Brande’s Encyclopedia; Ure's Dictionary • McCulloch f 
Commercial Dictionary ; Patent Office Reports. 



SCHEDULE OF PHILOSC PHICAL APPARATUS 

USED IN THE GRAMMAR-SCHOOLS OF THE CITY OF BOSTON.* 


LAWS OF MATTER. 

Apparatus for illustrating Inertia. 

Pair of Lead Hemispheres for Cohesion. 

Pair of Glass Plates for Capillary Attracticn. 

LAWS OF MOTION. 

Ivory Balls on Stand for Collision. 

Set of eight Illustrations for Centre of Gravity. 

Sliding Frame for Composition of Forces. 

Apparatus for illustrating Central Forces. 

MECHANICS. 

Complete set of Mechanicals, consisting of Levers, Pulleys, Wheei tin! 
Axle, Capstan, Screw, Inclined Plane, Wedge. 

HYDROSTATICS. 

Bent Glass Tube for Fluid Level. 

Mounted Spirit Level. 

Hydrometer and Jar for Specific Gravity. 

Scales and Weights for Specific Gravity. 

Hydrostatic Bellows, and Paradox. 

HYDRAULICS. 

Lifting, or Common Water-pump. 

Forcing Pump ; illustrating the Fire-engine. 

Glass Syphon-cup for illustrating intermittent Springs. 

Glass and Metal Syphons. 

PNEUMATICS. 

Patent Lever Air-pump and Clamp 

Three Glass Bell Receivers, adapted to the Apparatus. 

Condensing and Exhausting Syringe. 

Copper Chamber for Condensed Air Fountain. 

Revolving Jet and Glass Barrel. 


* T^e cost of this apparatus is about two hundred A seventy five dollars. It was made by 
Mr. Joseph M. Wightman, importer and manufacturer of Philosophical Apparatus, No 
33 Cornliill, Boston, and in an eminent degree unites beauty with durability. Messrs 
Chamberlain & Ritchie, also, in Washington-street, excel in their manufacture of Philo¬ 
sophical Instruments of all kinds. In the department of Electricity and Magnetism, Messrs. 
Palmer & Hall, successors of Darnel Davis 428 Washington-street, have many articles of 
excellent design and execution. 





PHILOSOPHICAL APPARATUS. 


M 


fount*.cu Glass, Cock, and Jet for Vacuum. 
Brass Magdeburg Hemispheres. 

Improved Weight-lifter for upward pressure, 
[ron Weight of fifty-six pounds, and Strap, ) 
Flexible Tube and Connectors, $ 

Brass Plate and Sliding 
Bolt Head and Jar. 

Tall Jar and Balloon. 

Hand and Bladder Glasses. 

Weed Cylinder and Plate. 

India-rubber Bag for expansion of air 
Guinea and Feather Apparatus. 

Glass Flask and Stop-cock for weighing 


for Weight-lifter 


ELBOTKIfUtv. 

Plate Electrical Machine. 

Pith-ball Electrometer. 

Electrical Battery of fi ar Jars. 

Electrical Discharger. 

Image Plates and Figure. 

Insulated Stool. 

Chime of Bells. 

Miser’s Plate for shocks. 

Tissue Figure, Ball and Point 
Electrical Flyer and Tellurian. 

Electrical Sportsman, Jar and Birds. 

Mahogany Thunder-house and PistoL 
Hydrogen Gas Generator. 

Chains, Balls of Pith, and Amalgam. 

OPTICS. 

Glass Prism, and pair of Lenses. 

Dissected Eyeball, showing its arrangement 

MAGNETISM. 

Magnetic Needle on Stand. 

Pair of Magnetic Swans. 

Glass Vase for Magnetic Swans. 

Horseshoe Magnet. 

ASTRONOMY. 

Improved School Orrery. 

Tellurian, or Season Machine. 

ARITHMETIC AN19 GEOMETRl. 

Set of thirteen Geometrical Figures of Solids. 

Box of sixty-four one-inch Cubes for Cube Root, &<> 

AUXILIARIES. 

Tin Oiler ; Glass Funnel ; Sulphuric Acid. 

Set of Iron Weights for Hydrostatic Paradox. 


CONTENTS 


Divisions of the Subject, ... 

Of Matter and its Propertied 

Of Gravity,.. , . 

Mechanics, or the Laws of motion, 
The Mechanical Powers, . . 

Regulators of Motion,. 

Hydrostatics, . 

Hydraulics,.. 

Pneumatics,. 

Acoustics,.. 

Pyronomics,.. 

The Steam-engine,. 

Optics,. 

Electricity,. 

Galvanism, or Voltaic Electricity, 

Magnetism,. 

Electro-Magnetism,. 

The Electro-magnetic Telegraph, . 

The Electrotype Process,. 

Magneto-Electricity .. 

Thermo-Electricity ....... 

Astronomy, . . P .. -» , . 


IT 

IS 

33 

41 

70 

100 

108 

128 

138 

173 

185 

196 

210 

258 

283 

298 

308 

319 

331 

332 

334 

335 


The Index at the close of the volume, being lull and comprencnslve, will t* found inon 
wnveuleut to' reference. 

























INTRODUCTION. 


The term Philosophy literally signifies, the love of wisdom ; 
but, as a general term, it is used to denote an explanation of the 
reason of things, or an investigation of the causes of all phenomena, 
both of mind and of matter. 

When applied to any particular department of knowledge, the 
word Philosophy implies the collection of general laws or princi¬ 
ples, under which the subordinate facts or phenomena relating to 
that subject are comprehended. Thus that branch of Philosophy 
which treats of God, his attributes and perfections, is called Theol¬ 
ogy ; that which treats of the material world is called Physics, 
or Natural Philosophy; that which treats of man as a rational 
being is called Ethics, or Moral Philosophy; and that which treats 
of the mind is called Intellectual Philosophy, or Metaphysics. 

The word Theology is derived from two Greek words, the 
former of which (©eos) signifies God, and the latter ( loyo <) means 
a discourse; and these two words, combined in the term Theology, 
literally imply a discourse about God. The latter of these two 
Greek words (loyos or logos) is changed into logy to form English 
compounds, and it enters into the composition of many scientific 
terms. Thus we have the words mineraZog'y, the science of miner¬ 
als; meteoroZog'y, the science which treats of meteors; ichthyoZog-y. 
the science of fishes ; entomoZog’y, the science of insects; lithoZo^y, 
of stones ; conchoZogy, of shells, &c. 

The word Metaphysics is composed of two Greek words, Meta 
(or //era), which signifies beyond, and phusis (or (pvon ), which 
signifies nature , and in composition these words imply something 
‘Z 



INTRODUCTION. 


AiV 

beyond 'nature . From the latter of these words, phusis 
we obtain the term physics , which in its most extended sense 
implies the science of nature and natural objects, comprehending 
the study or knowledge of whatever exists. The natural division 
of all things that exist is into body and mind — things material 
and immaterial, spiritual and corporeal. Physics relates to mate¬ 
rial things, Metaphysics -to immaterial. Man, as a mere animal, 
is included in the science of Physics; but, as a being possessed of a 
soul, of intellect, of the powers of perception, consciousness, volition, 
reason, and judgment, he becomes a subject of consideration in the 
science of Metaphysics. 

All material things are divided into two great classes, called 
organized and unorganized matter. Organized matter is that 
which is endowed with organs adapted to the discharge of appro¬ 
priate functions, such as the mouth and stomach of animals, or the 
leaves of vegetables. By means of such organs they enjoy life. 
Unorganized matter, on the contrary, possesses no such organs, 
and is consequently incapable of life and voluntary action. Stones, 
the various kinds of earth, metals, and many minerals, are in¬ 
stances of unorganized matter. Fossils, that is, substances dug 
out of the earth, are frequently instances of a combination of 
organized and unorganized matter. Unorganized matter also 
enters into the composition of organized matter. Thus, the bones 
of animals contain lime, which by itself is unorganized matter. 

Physical Science, or Physics, with its subdivisions of Natural 
History (including Zoology, Botany, Mineralogy, Conchology, 
Entomology, Ichthyology, &c.) and Natural Philosophy, including 
its own appropriate subdivisions, embraces the whole field of organ¬ 
ized and unorganized matter. 

The term Natural Philosophy is considered by some authors as 
embracing the whole extent of physical science, while others use it 
in a more restricted sense, including only the general properties 
of unorganized matter, the forces which act upon it, the laws which 
it obeys, the results of those laws, and all those external changes 
which leave the substance unaffected. It is in this sense that the 
term is employed in this work 


INTRODUCTION. 


XV 


Chemistry, on the contrary, is the science which investigates 
. the composition of material substances, the internal changes whie 
they undergo, and the new properties which they acquire by sue 
changes. The operations of chemistry may be described under tl 
heads of Analysis or decomposition, and Synthesis or combination 

Natural Philosophy makes u3 acquainted with the condition an 
relations of bodies as they spontaneously arise, without any agent t 
of our own. Chemistry teaches us how to alter the nature 
arrangement of elements to bring about some particular conditio: 
that we desire. To accomplish these objects in both of the depart¬ 
ments of science to which we refer, we make use of appliances 
called philosophical and chemical apparatus, the proper use of 
which it is the office of Natural Philosophy and Chemistry respect¬ 
ively to explain. All philosophical knowledge proceeds either 
from observation or experiment, or from both. It is a matter of 
observation that water, by cold, is converted into ice; but if, by 
means of freezing mixtures, or evaporation, we actually cause water 
to freeze, we arrive at the same knowledge by experiment. 

By repeated observations, and by calculations based on such 
observations, we discover certain uniform modes in which the 
powers of nature act. These uniform modes of operation are called 
laws ; — and these laws are general or particular according to the 
extent of the subjects which they respectively embrace. Thus, it 
is a general law that all bodies attract each other in proportion to 
the quantity of matter which they contain. It is a particular law 
of electricity that similar kinds repel and dissimilar kinds attract 
each other. 

The collection, combination, and proper arrangement of such 
general and particular laws, constitute what is called Science. 
Thus, we have the science of Chemistry, the science of Geometry, 
the science of Natural Philosophy, &c. 

The terms art and science have not always been employed with 
proper discrimination. In general, an art is that which depends 
on practice or performance, while science is the examination of 
general laws, or of abstract and speculative principles. The theory 
of music is a science; the practice of it is an art. 


XVi 


INTRODUCTION. 


Science differs from art in the same manner that knowledge 
differs from skill. An artist may enchant us with his skill, 
although he is ignorant of all scientific principles. A man of 
science may excite our admiration by the extent of his knowledge, 
though he have not the least skill to perform any operation of art,. 
When we speak of the mechanic arts, we mean the practice of 
those vocations in which tools, instruments and machinery, are 
employed. But the science of Mechanics explains the principles 
on which tools and machines are constructed, and the effects which 
they produce. Science, therefore, may be defined, a collection and 
proper arrangement of the general principles or leading truths 
relating to any subject; and there is this connection between art 
aid science, namely — “ A principle in science is a rule of art.” 


NATURAL PHILOSOPHY 


DIVISIONS OF THE SUBJECT. 


1. Natural Philosophy, or Physics, is the 

What is 7 \ 

Natural science which treats ot the powers, properties and 

Philo so- mu tual action of natural bodies, and the laws and 

operations of the material world. 

i. Some of the principal branches of Natural Philosophy are 
Mechanics, Electricity, 

Pneumatics, Galvanism, 

Hydrostatics. Magnetism, 

Hydraulics, Electro-Magnetism, 

Acoustics, Magneto-Electricity, 

Pyronomics, Astronomy. 

Optics, 

— This list of branches might be considerably enlarged, but per¬ 
haps a rigid classification would rather suggest the omission of some of 
them, as pertaining to the department of chemistry. 


What is 


3. Mechanics. —Mechanics is that branch of 
Meehan- Natural Philosophy which relates to motion and 
ics ' the moving powers, their nature and laws, with 
their effects in machines. 

4. Mechanics is generally considered under two division*, culled 
Statics and Dynamics. 



18 


NATURAL PHILOSOPHY. 


*■ 

5. The word Statics is derived from a Greek word implying rest 
and it is applied to that department of mechanics which treats of 
the properties and laws of bodies at rest. 

6. Dynamics, from a Greek word signifying power or force 
Ireats of the properties and laws of bodies in motion. 

7. Pneumatics treats of the mechanical properties and effects 
of air arid similar fluids, called elastic fluids or gases. 

8. Hydrostatics treats of the gravity and pressure of fluids in 
a state of rest. 

9. Hydraulics treats of fluids in motion, and of the instru¬ 
ments and machines by which their motion is guided or con¬ 
trolled. 

10. Acoustics treats of the laws of sound. 

11. Pyronomics treats of the laws and effects of heat. 

12. Optics treats of light, color and vision. 

13. Electricity treats of an exceedingly subtle agent, jailed 
the electric fluid. 

14 Galvanism (sometimes called chemical ( lectricity) is a 
branch of Electricity. 

15. Magnetism treats of the properties and effects of the 
magnet or loadstone. 

16. Electro-Magnetism treats of magnetism inc uced by elec¬ 
tricity. 

17. Magneto-Electricity treats of electricity induced by mag¬ 
netism. 

18. Astronomy treats of the heavenly bodies,—the sun, moon, 
stars, planets, comets. 

19. The agents whose efleets or operations are described m 
Natural Philosophy are divided into two classes, called respectively 
Ponderable and Imponderable Agents. 

Note. — Some writers on Philosophy have suggested a different classi¬ 
fication, into Bodies and Agents, calling bodies potulerablc, and agents im¬ 
ponderable. 

20. Ponderable agents are.those which have weight, as watei, 
air, steam. 

21. Imponderable agents are those which have no weight such 
u& iiglifc heat, magnetism and electricity. 


OF MATTER AND ITS PROPERTIES. 


19 


What n 22. Matter. — Matter is the general name of 
Matter? everything that occupies space. 

23. Matter exists in four different states or forms, namely 
in the solid, liquid, gaseous and vesicular forms. 

24. Matter exists in a solid form when the particles of which it is 
composed cohere together. The different degrees of cohesion which 
different bodies possess causes them to assume different degrees of 
hardness. 

25. Matter exists in a liquid state when the component parts do 
not cohere with sufficient force to prevent their separation by the 
mere influence of their weight v The surface of a fluid at rest always 
conforms itself to the shape of the portion of the earth’s surface 
over which it stands. 

26. Matter exists in a gaseous or aeriform state when the par¬ 
ticles of which it is composed have a repulsion towards each other 
which causes them to separate with a power of expansion to which 
there is no known limit. Of this, smoke presents a familiar in¬ 
stance. As it ascends it expands, the particles repelling each other 
until they become wholly invisible. 

Note. —The word aeriform means, in tke form of air. 

27. The vesicular form of matter is the form in which we see it 
in clouds. It consists of very minute vesicles, resembling bubbles, 
and it is the state into which many vapors pass before they assume 
a fluid condition. 

28. Some substances are capable, under certain conditions, of 
assuming all these different forms. Water, for instance, is solid in 
the form of ice, fluid as water, in the gaseous state when converted 
into steam, and vesicular in the form of clouds. 

29. All matter, whether in the solid, liquid, gaseous, or vesiculai 
form, is either simple or compound in its nature. But this consider¬ 
ation of matter pertains more properly to the science of chemistry. 
It is proper, however, here to explain what is meant by a simple or 
homogeneous and a compound or heterogeneous substance. 

30. All matter is composed of very minute particles or atoms 
united together by different degrees of cohesion. When all the 
atoms are of the same kind, the body is a simple or homogeneous 
substance. Thus, for instance, pure iron, pure gold, &c., consists 
of very minute particles or atoms, all of which are pure iron or 
pure gold. But water, and many other substances, are compound 
Bubstances, composed of atoms of two or more different substances, 
combined by chemical affinity. 

Note. — The ancient philosophers supposed that all material substances 
vere composed of Fire, Air, Earth and Water, anJ these four substances 
Btire called the f ur elements, because they were supposed to be the siuivlt 


i!0 


NATURAL PHILOSOPHY. 


substances of which all things are composed. But modern science h»« 
shown that not one of these is a simple substance. Water, for instance, is 
composed of two invisible gases, called Hydrogen and Oxygen, united in the 
proportion of one part, in weight, of hydrogen to eight of oxj'gen ; or, by 
measure, one part of oxygon to two of hydrogen. In like manner air, or, 
rather, what the ancients understood by air, is composed of oxygen united 
with another invisible gas, called nitrogen or azote, in the proportion of 
seventy-two parts of the latter to twenty-eight of the former. 

The enumeration of the elementary substances, which, either by them¬ 
selves or in union with one another, mane up the material world, properly 
belongs to the science of chemistry. As this work may fall into the hands 
of some who will not find the information elsewhere, a list of the simple 
substances or elements is here presented, so far as modern science has 
investigated them. They are sixty-one in Dumber, forty-nine of which are 
metallic and twelve are non-metallic. 

The forty-nine metals are 


Gold, 

Silver, 

Iron, 

Copper, 

Tin, 

Mercury, 

Lead, 

Zinc, 

Nickel, 

Cobalt, 

Bismuth, 

Platinum, 

Antimony, 

Arsenic, 


Manganese, 

Cadmium, 

Uranium, 

Palladium, 

•Rhodium, 

Iridium, 

Osmium, 

Titanium, 

Coluinbium, 

Tellurium, 

Tungsten, 

Molybdenum, 

Vanadium, 

Chromium, 


Potassium, 

Sodium, 

Lithium, 

Barium, 

Strontium, 

Calcium, 

Magnesium, 

Aluminum, 

Glucinum, 

Y ttrium, 

Zirconium, 

Thorium, 

Cerium, 

Lantanium, 


The non-metallic elements are 
Oxygen, Sulphur, Chlorine, 

Hydrogen, Phosphorus, Bromine, 

Nitrogen, Carbon, Iodine, 


Didynium, 

Erbium, 

Terbium, 

Ruthenium, 

Pelopium, 

Niobium. 

Selenium. 

[ This substance is of <[ues 
tionable nature, some of 
its properties indicating n 
metallic and some a non- 
metallic character .] 

[The last seven, in Italic, 
have not yet been 
fully investigated. J 

Fluorine, 

Borax, 

Silica. 


Of the elementary'substances now enumerated, about fourteen constitute 
the great mass of our earth and its atmosphere. The remainder occur only 
in comparatively small quantities, while nearly a third of the whole number 
is so rare that their uses in the great economy of nature are not under¬ 
stood, nor have they as yet admitted of any useful application. 

The science of Geology reveals to us the fact that granite appears to be 
the foundation of the crust of the earth ; and in the granite, either in its 
original formation, or in veins or seams which have been thrown up by 
subterranean forces into the granite, all of the elementary substances which 
have been enumerated are to be found. A chart is presented below in 
which the materials composing the strata of the crust of the earth are 
enumerated, together with a tabular view of the composition of these 
materials. It is not contended that this chart is perfectly accurate in ail 
its details ; but, as it affords an interesting and extensive subject of inves¬ 
tigation, and as it is not to be found elsewhere in print, it is thought that 
it will be well worth the space which it occupies, although a rigiu cn»a» 
fieatiou would exclude it from this work. 


OF MATTER AND ITS PROPERTIES. 


2i 


,Pr. Beyntcn's Chart of Materials that enter into the Composition of tjranilt. 



Silica. 

‘Alumina. 

4 

1 

£h 

e$ 

% 

OQ 

Lime. 

Magnesia. 

Ox. Iron. 

Ox. Manganese. 

Water. 

| Carb. Acid. 


Quartz. 

100 











Feldspar ...... 

65 

19 

14 


1 


1 





Albite. 

70 

20 


10 








Mica. 

46 

26 

10 


1 

5 

8 

1 

2 


2 Fluor Acid 








Prot. 












Ox. 





Hornblende .... 

48 

12 



14 

19 

7 





Augite. 

54 

1 



24 

17 

4 





Diallage. 

47 

4 



13 

25 

8 


3 









M. 





Chlorite. 

27 

18 

2 



15 

31 


7 










Prot. 

■ 




Talo.. . 

57 

1 



4 

27 

8 


3 



Hypersthene .... 

56 

2 



2 

14 

25 


1 



Actynolite. 

56 

2 



12 

13 

17 











M. 





Steatite. 

62 

1 



1 

28 

2 


6 



Serpentine. 

42 




5 

33 

7 


13 



Schorl. 

36 

36 

1 

2 


5 

14 

2 



4 B. Acid 








Prot. 





Garnet .... . . 

40 

20 



1 


36 

3 











Prot. 

Prot. 




M. Garnet . . 

36 

18 





15 

31 




Clay. 

75 

10 



5 

2 

3 











Prot. 





Green Sand. 

48 

7 

j 8 




26 


11 



Carbonate of Lime . . 





56 






44 Carb. Acid. 

Carbonate of Magnesia 






48 



2 


50 «« « 


What are 
the essen¬ 
tial Prop¬ 
erties of 
Matter ? 


31. There are seven essential * properties be- 
longing to matter, namely, 1. Impenetrability 
2. Extension; 3. Figure; 4. Divisibility; 5. In- 
destructibility; 6. Inertia; 7. Attraction. 


What is 32. Impenetrability. — Impenetrability is the 
inability ? power of occupying a certain portion of space, so 


* An essential property of a body is that which is necessary to the 
absolute existence of the body. All matter in common possesses these 
essential properties, and no particle of matter can exist without any *ne of 
them. Different bodies possess other different properties which are not 
essential to their existence, such as color, weight, brittleness, hardness; 
Ac. These are called accidental properties, as they depend on circuw 
nces not essential to the very existence of a body. 











































l‘l NATURAL PHILOSOPHY. 

that where one body is another cannot be without dis¬ 
placing it. 

83. This property, Impenetrability, belongs to all bodies and 
forms of matter, whether solid, fluid, gaseous, or vesicular. 

The impenetrability of common air may be shown by immera ng 
an inverted tumbler in a vessel of water. The air prevents the 
water from rising into the tumbler. An empty bottle, also, forcibly 
held horizontally under the water, will exhibit the same property , 
for the bottle, apparently empty, is filled with air, which escapes 
in bubbles from the bottle as the water enters it. But, if the bottle 
be inverted, the water cannot enter the bottle, on account of the 
impenetrability of the air within.* 


* This circumstance explains the reason why water, or any other liquid, 
poured into a tunnel closely inserted in the mouth of a decanter, will run 
over the sides of the decanter. The air filling the decanter, and having 
no means of escape, prevents the fluid from entering the decanter ; but, if 
the tunnel be lifted from the decanter but a little, so as to afford the air an 
opportunity to.escape, the water will then flow into the decanter in an un¬ 
interrupted stream. 

"When a nail is driven into wood or any other substances, it forces the 
particles asunder and makes its way between them. 

An experiment was made at Florence, many years ago, to show the im¬ 
penetrability of water. A hollow globe of gold was filled with water and 
(subjected to great pressure. The water, having no other means of escape, 
was seen to exude from the pores of the gold. 

The reason why fluids appear less impenetrable than solids is that the 
particles which compose the fluids move easily among themselves, on account 
of their slight degree of cohesion, and when any pressure is exerted upon a 
fluid the particles move readily into the unoccupied space to which they 
have access. But, if the fluid be surrounded on all side3, and have no 
means of escape, it will be found to possess the property of impenetrability 
in no less a degree than solid .bodies. 

A well-known fact seems, at first view, to be at variance with this state¬ 
ment. When a vessel is filled to the brim with water or other fluid, a con¬ 
siderable portion of salt may be dropped into the fluid without causing the 
vessel to overflow. And, when salt has been added until the water can 
hold no more in solution, a considerable quantity of sugar can be added in 
a similar manner. The explanation of this familiar 
fact is as follows The particles of the sugar are 
smaller than the particles of the salt, and the particles 
of the salt are smaller than the particles which compose 
the water. Now, supposing all of these particles to be 
globular, they will arrange themselves as is represented 
in Fig. 1, in which the particles of the water are indi¬ 
cated by the largest circles, those of the salt by the 
next in size, and those of the sugar by the smallest. 

Fainillar Experiment. — Fill a bowl or tumbler with peas, then pour on 
the peas mustard-seed or fine grain, shaking the vessel to cause it to fill the 
vacant spaces between the peas. In like manner add, successively, fine sand, 
water, salt and sugar. This will afford an illustration of the apparent paradox 
uf two bodies occupying the same space, and show that it is only apparent. 


Fig. 1. 



of matter am> m> pkoieutiks. 


34. Extension. — Extension is but another 
name for bulk or size, and it is expressed by the 
terms length, breadth or width, height, depth and 
th.ehuim 

Note. -- Length is the extent from end to end. Breadth or width is the 
extent from side to side. Height, depth or thickness, is the extent from 
the top to the bottom. The measure of a body from the bottom to tho top 
is called height ; from the top to the bottom, is called depth. Thus we 
speak of the depth of a well, the height of a house, Ac. 

Figure’ S5 ‘ Figure is the form or shape of a body. 

36. Figure and Extension are separate properties, although both 
may be represented by the same terms, length, breadth, &c. But 
they differ as the words shape and size differ. Two bodies may be 
of the same .figure or shape, but of vastly different size. A grape and 
an orange resemble each other in shape, but differ widely in size. 
The limits of extension constitute figure, but figure' has no other 
connexion with extension. 

What is 37. Divisibility.— Divisibility is susceptibility 
bility? of being divided. 

38. To the divisibility of matter there is no known limit, nor 
can we conceive of anything so small that it is not made up of two 
halves or four quarters. It is indeed true that our senses are quite 
limited in their operation, and^that we cannot perceive or take 
cognizance, by means of our senses, of many objects of the existence 
of which we are convinced without their immediate and direct 
testimony. 

39. Sir Isaac Newton has shown that the thickest part of a soap- 
bubble does not exceed the two-millionth part of an inch. 

40. The microscopic observations of Ehrenberg have proved that 
there are many species of little creatures, called Infusoria , so small 
tnat millions of them collected into a single mass would not exceed 
the bulk of a grain of sand, and thousands of them might swim 
side by side through the eye of a small needle. , 

41. In the slate formations in Bohemia these little creatures aro 
found in a fossil state, so small that it would require a hundred and 
eighty-seven millions of them to weigh a single grain. 

42. A single thread of the spider’s web has been found to be 
composed of six thousand filaments. 

43. A single grain of gold may be hammered by a gold-beater 
until it will cover fifty square inches ; each square inch may bo 
divided into two hundred strips ; and each strip into two hundred 
rarts. One of these parts is only oik two-millionth part of a grain 
;f gold, and yet it may be seen with the naked eye 


Wi <. 

LXI* 
non ? 


NATURAL PHILOSOPHY. 

44. The particles which escape from odoriferous objects ftmo 
afiord instances of extreme divisibility. 

/I/e-* U 45. Indestructibility. — By the Indestructi- 

siructi- bility of matter is meant that it cannot be destroyed. 
bility ? J J 

46. A body may be indefinitely divided or altered in its form, 
color, and other unessential properties, but it can never be destroyed 
by man. It must continue to exist in some form, with all its 
essential properties, through all its changes of external appearance. 
He alone “ who can create can destroy.” 

47. When water disappears, either by boiling over a fire or by 
evaporation under the heat of the sun, it is not destroyed, but 
merely changed from a liquid to a fluid form, and becomes steam or 
vapor. Some of its unessential properties are altered, but its essential 
properties remain the same, under all the changes which it under¬ 
goes. In the form of water it has no elasticity * and but a limited 
degree of compr-sm bility.* But when “ it dries up” (as it is 
called) it rises in the form of steam or vapor, and expands to such a 
degree as to become invisible. It then assumes other properties, 
not possessed before (such as elasticity and expansibility); it ascends 
In the air and forms clouds ; these clouds, affected by the temperature 
of the air and other agents, again fall to the earth in the form of 
rain, hail, snow or sleet, and form springs, fountains, rivers, &c 
The water on or in the earth, therefore, is constantly changing its 
3Lape or situation, but no particle of it is ever actually destroyed. 

48. Substances used as fuel, whether in the form of wood, coal. 
27 other materials, in like manner undergo many changes by the 
'process of combustion. Parts of them rise in the form of smoke, 
part ascends in vapor, while the remainder is reduced to the form 
of ashes ; but no part is absolutely destroyed. Combustion merely 
disunites the simple substances of which the burning materials are 
composed, forming them into new combinations ; but every part still 
continues in existence, and retains all the essential f properties of 
bodies. 

What is 49. Inertia. — Inertia J is the resistance of 
Inertia ? matter to a change of state, whether of motion or 
of rest. 

* Late writers assert that water has a slight degree r<Xii cf elasticity and 
expansibility. 

t The reader will be careful to carry in his mind what is meant by the 
term an essential property . It is explained in the note to No. 31, page 21 

X The literal meaning of inertia is inactivity, and implies inability tc 
change a state of rest or of motion. A clear and distinct understanding o 1 
tliis property of all matter is essential in all the departments cf material 
philosophy. All matter, mod* mically considered, must be in a state either 


OF MATTER AND ITS PROPERTIES. 


2n 


MV A body at rest cannot put itself in motion, nor can a body 
m motion stop itself This incapacity to change its state from reel 
to motion, or from motion to a state of rest, is what is implied by 
the term inertia. 

51. It follows, therefore, from what has just been stated, that 
when a body is in motion its inertia w r ill cause it to continue to move 
until its motion is destroyed by some other force. 

52. There are two forces constantly exerted around us which 
tend to destroy motion, namely, gravity and the resistance of the air. 
All motion caused by animal or mechanical power is affected by 
these two forces. Gravity (which will presently be explained) 
causes all bodies, whether in motion or at rest , to tend towards the 
centre of the earth, and the air presents a resistance to all bodies 
moving in it. Could these and all other direct 
obstacles to motion be set aside, a body when 
once put in motion would always remain in 
motion, and a body at rest, unaffected by any 
external force, would always remain at rest.* 

53. Experiment to illustrate Inertia .— 

Fig. 2 represents the simple apparatus of 
Mr. Wightman for illustrating the inertia 
of a body. A card is placed on the top of 
a stand, and a ball is balanced on the card. 

of motion or rest ; ^nd, in whatever state ft may be, it must remain in that 
state until a change is effected by some rfiicient cause, independent of the 
body itself. A body placed upon anothrr body in motion partakes of the 
motion of the body on which it is plaeod. But, if that body be suddenly 
stopped, the superincumbent body will not stop at the same time, unless it 
be securely fastened. Thus, if a hors*' 1 , moving at a rapid rate be suddenly 
stopped, the rider will be thrown forward, on account of this inertia of his 
body, unless by extra exertion he secures himself on the saddle by bracing 
his feet on the stirrups. On the contrary, if the horse, from a state of rest, 
start suddenly forward, the rider will be thrown backwards. For the same 
reason, when a person jumps from a vehicle in motion to the ground, his 
body, partaking of the motion of the vehicle, cannot be suddenly brought 
to a state of rest by his feet resting on the ground, but will be thrown 
forward in the direction of the motion which it has acquired from the 
vehicle. This is the reason that so many accidents happen from leaping 
from a vehicle in motion. 

* In the absence of all positive proof from the things around us ot 
the statement just made, we may find from the truths which astronomy 
teaches that inertia is one of the necessary properties of all matter. Tin? 
heavenly bodies, launched by the hand of their Creator into the fields of 
infinite space, with no opposing force but gravity alone, have performed 
their stated revolutions in perfect consistency with the character which 
this property gives them ; and all the calculations which have been made 
with respect to them, verified as they have repeatedly been by observation, 
have been predicated on their possesion of this necessary pro^-crty of all 
matter. 


Fig. 2. 



A quick' motion is 




26 


NATURAL PHILOSOPHY 


then given to the card by means of a spring, and the card flies 
off, leaving the ball on the top of the stand.* 

54. Nature seems to have engrafted some knowledge of mechan¬ 
ical laws on the instinct of animals. When an animal, and especially 
a large animal, is in rapid motion, he cannot (on account of the 
inertia of his body) suddenly stop his motion, or change its direction; 
and the larger the animal the more difficult does a sudden stoppage 
become. The hare pursued by the hound often escapes, when the 
dog is nearly upon him, by a sudden turn, or changing the direction 
of its flight, thus gaining time upon his pursuer, whose inertia's not 
so readily overcome, and who is thus impelled forward beyond the 
spot where the hare turned. 

55. Children at play are in the same manner enabled “ U j/uige” 
their elder playmates, and the activity of a boy will often enable 
him to escape the pursuit of a man. 

56. It is the effect of inertia to render us sensible to motion. A 
person in motion would be quite unconscious of that state, were it 
Qot for the obstacles which have a tendency to impede his progress. 
In a boat on smooth water, motion is perceptible only by the 
apparent change in the position of surrounding objects : but, if the 
course of the boat be interrupted by running aground, or striking 
against a rock, the person in the boat would feel the shock caused 
by the sudden change from a state of motion to a state of rest, and, 
unless secured to his seat in the boat, lie would be precipitated 
forward 

What is At - 57. Attraction.— Attraction is the tendency 

traction ? which different bodies or portions of matter 
have to approach or to adhere to each other. 

What is the 58. Every portion of matter is attracted by every 
Miv of At- other portion of matter, and this attraction is the 
raction . B t r0 nger in proportion to the quantity and the dis¬ 
tance. The larger the quantity and the less the distance, the 
stronger is the attraction.! 


* The ball remains on the pillar in this case not solely from its inertia 
but because sufficient motion is not communicated to the boll by the fric¬ 
tion of the card to counteract the effect of gravity on the ball. If the 
bail, therefore, be not accurately balanced on the card, the experiment will 
act be successful, because the card cannot move without communicating at 
least a portion of its motion to the ball. 

t [N. B. This subject will be more fully treated under the head of 
jftatri jty See page 33.] 


OF MATTER AND ITS PROPERTIES. 


27 


(mo many 59. There are two kinds of attraction, namely 
fciW„ of At- -i » . „ ~ . . . . ’ J 5 

‘ract.on are ttie Attraction of Gravitation and the Attraction 

’kere * 0 f Cohesion. 

The former belongs to all matter, whatever its form, the 
latter appears to belong principally to solid bodies. 

What ts the 60. The Attraction of Gravitation is the 
Attraction . ,, . » . „ 

of Gravi- reciprocal attraction of separate portions of 

tation t matter. 


What is the 
Attraction 
of Cohesion t 


61. The Attraction of Cohesion is that which 
causes the particles of a body to cohere together. 
[See No. 31.] 


62. The attraction of cohesion appears to exist but in a very 
slight degree, if at all, in liquids arid fluids. 

Exemplify 

the two kinds 63. The attraction of gravitation causes a body, 

Uon^name w ^ ien unsupported, to fall to tire ground. The 

ly, Gravity attraction of cohesion holds together the particles 

and Cohesive 0 f a body an d causes them to unite in masses.* 
Attraction? J 


64. Having described the essential properties of bodies, we 
come now to the consideration of other properties belonging respect¬ 
ively to different kinds of matter ; such as Porosity, Deusity, Rarity, 
Compressibility, Expansibility. Mobility, Elasticity, Brittleness, 
Eloxibility, Malleability, Ductility, Tenacity. 

65. It has already been stated that matter consists of minute 
particles or atoms, united by different degrees of cohesive attraction. 
These atoms are probably of different shapes in different bodies, and 
the different degrees of compactness with which they unite give 
rise to certain qualities, which differ greatly in different substances 
These qualities or properties are described under the names of 
Porosity, Density and Rarity, which will presently be described. 


* Besides tbeso two kinds of attraction, thert- seem to be other kinds 
ot attractive force, active in vegetation and in animal life, known by the 
names of Endosmose and Exosmo.se, terms applied to the transmission of 
gs^eous matter or vapors through membranous substances. See note to 
Capillaiy Attraction, under the head of Hydrostatics, on page 112. 

Other kinds of attraction, called Electrical and Magnetical Attraction, 
will hereafter be considered under their appropriate head. The subject of 
Chemical Attraction or Affinity belongs distinctly to the subject of Chemistry 
and will not, therefore, be considej od in this work 


•28 


NATURAL PHILOSOPHY. 


66. Besides the property of attraction possessed by cne particles 
or atoms of which a body- is composed, there seems to be another 
property, of a nature directly opposite to attraction, which exerts 
itself with a repulsive force, to prevent a closer approximation of 
the particles than that which by the law of their nature they assume. 
This property is called repulsion. This repulsion prevents the par¬ 
ticles or atoms from coming into perfect contact, so that there must 
be small spaces between them, where they do not absolutely touch 
one another. [See Figure ls^.j These spaces are called pores, n nd 
where they exist give rise to that property or quality described 
under the name of Porosity. 

What is 67. Porosity. — Porosity implies, therefore, that 
Porosity ? there are spaces, or pores , between the particles or 
atoms which form the mass of a body. 

68. Density.— When the pores are few, so that a large number 

of particles uuite in a small mass, the body is called a dense body. 

What is 69. Density, therefore, implies the closeness or 

Density ? compactness of the particles which compose any 
substance. 

70. Rarity. — When the pores in any substance are numerous, 
so that the particles which form it touch one another in only a few 
points, the body is called a rare body. 

What is 71. Rarity, therefore, is the reverse of density, 
Rarity 1 an d implies extension of bulk without increase in 
the quantity of matter. 

72. From wdiat has now been stated it appears [See No. 67] that 
the particles of a body are connected together by a system of attrac¬ 
tions and repulsions which give rise to distinctions which have 
already been described. It remains to be stated that these attractions 
and repulsions differ much in degree in different substances, and this 
difference gives rise toother properties, which will now be explained, 
under their appropriate names. 

73. Compressibility. —When the repulsion of the particles of any 
substance can be overcome and the mass can be reduced w’ithin 
narrower limits of extension, it is said to possess the property of 
Compressibility.* 

* Compressibility differs from Contractibility rather in cause than In 
effect. Contractibility implies a change of bulk caused by change of 
temperature, or any other agency not mechanical. Compressibility implies 
6hut the diminution of bulk is caused by some external mechanical force 


OF MATTER AND ITS PROPERTIES. 


29 


v\hat is 74. Compressibility, therefore, may be defined, the 
Compres ■ susceptibility of a reduction of the limits of ex* 
tension. L 

75. This property is possessed by all known substances, but in 
very different degrees,-—some substances requiring but little force 
to compress them, others resisting very great forces ; but it is not 
known that there is any substance unsusceptible of compression, if 
a sufficient force be applied * 

76. Liquids in general are less easily compressed than solid 
bodies; so much so, indeed, that in practical science they are gen¬ 
erally considered as incompressible. Under a very considerable 
mechanical force, a slight degree of compression has been observed.j 

77. Expansibility. —The system of attractions and repulsions 
among the particles of a body are sometimes so equally balanced 
that they exist, as it were, in an equilibrium. In other cases the 
repulsive energy is so great as to predominate when the attractive 
force is unaided. When the repulsive energy is permitted to act 
without restraint, it forces the particles asunder and increases the 
limits of extension, giving rise to another property of matter 
possessed by many bodies, but in an eminent degree by matter in a 
gaseous form. This property is called Expansibility. 

78. Expansibility ,% therefore, may be defined 
as that property of matter by which it is enabled 
to increase its limits of extension. 

79. Elasticity. — When the atoms or particles which constitute 
a body are so balanced by a system of attractions and repulsions 
that they resist any force which tends to change the figure of the 


Expansi¬ 
bility ? 


* Sir Isaac Newton conjectured that if the earth were so compressed 
as to be absolutely without pores, its dimensions might not exceed a cubic 
inch. 

f Under a pressure of fifteen pounds on a square inch, water has been 
diminished in bulk only by about forty-nine parts in a million. Under a 
pressure of fifteen thousand pounds cn a square inch, it was compreased 
by about one-twentieth of its volume. The experiment was tried in a cannon, 
and the cannon was burst. 

f: Expansibility and Dilatability are but different names for the same 
property ; but expansion implies an augmentation of the bulk or volume, 
dependent on mecnanical agency, while dilatation expresses the same 
condition produced by some physical cause not properly falling under the 
denomination of mechanical force. Thus heat dilates most substances, 
while cold contracts them. It is on this principle that the thermometer is 
constructed. [See page 149, No. 546.] 

All gaseous bodies are invested with the property of rlilntahility to an 
unlimited degree, by means of which, when unrestrained, they will expand 
spontaneously, and that without the application of any external agency, to 
a degree to which there is no known limit, 
ii it- 


30 


NATURAL PHILOSOPHY. 


body, they will possess another property, known by the name of 
Elasticity. 

80. Elasticity, therefore is the property which 
causes a body to resume its shape after it has been 
compressed or expanded.* * * § 

81. Thus, when a bow or a steel spring is bent, its elasticity 
causc3 it to resume its shape. 

82. India rubber (or caoutchouc) possesses the property of 
elasticity in a remarkable degree, but steam and other bodies in 
a gaseous form in a still greater.t 

83. Ivory is endowed with the property of elasticity in a remark 
able degree, but exhibits it not so much by the mere force of pressure, 
dut it requires the force of impact to produce change of form.J 

What is 84. Brittleness. — Brittleness implies aptness 
ness? to break into irregular fragments.$ 

* This property is possessed, in at least some small degree, by all sub¬ 
stances ; or, at least, it cannot be said that any substance is wholly 
destitute'of elasticity. Even water and other liquids, which yield with 
difficulty to compression, recover their volume with a force apparently 
equal to the compressing force. But, for most practical purposes, many 
substances, such as putty, wet paste, moist paper, clay, and similar bodies, 
afford examples of substances possessing the property of elasticity in so 
slight a degree that they are treated as non-elastic bodies. 

f The gases or aeriform bodies afford the most remarkable instances 
of elasticity. When water is converted into steam it occupies a space 
seventeen hundred times greater than the water from which it is formed, and 
its elasticity causes it to expand to still larger dimensions on the application 
bf heat. It is this peculiar property of steam, modified, as will be explained 
in a future part of this work, which is the foundation of its application in 
the movement of machinery. All gaseous bodies are equally elastic. 

I The metals which are best adapted to produce sound are those 
which are most highly elastic. It sometimes happens that two metals, 
neither of which have any great degree of hardness or elasticity, when 
combined in certain proportions, will acquire both of these properties. 
Thus tin and copper, neither of which in a pure state is hard or elastic, 
when mixed in a certain proportion, j^roduce a compound so hard and 
elastic that it is eminent for its sonorous property, and is used for making 
bells, 

§ Brittleness and hardness are properties which frequently accom¬ 
pany each other, and brittleness is not inconsistent with elasticity. Thu 
glass, for instance, which fs the most brittle of all known substances, i. 
hignly elastic. The same body may acquire or be divesteu of its brittle¬ 
ness according to the treatment which it receives. Thus iron, and some 
other metals, when he?ted and suddenly plunged into cold water, become 
brittle; but if, in a heated state, they are burned in hot sand, and thus no 


What is 
Elastic- 
tty? 


OE MATTER AND ITS PROPERTIES. 


3! 


What is 
Flexi¬ 
bility? 


85. Flexibility. — Flexibility implies a dis- 
position to yield withe ut breaking when bent. 


86. Malleability. — Malleability implies that 
property by means of which a body may be re¬ 
duced to the form of thin plates by means of the 
hammer or the pressure of rollers. 


What is 
Mallea¬ 
bility ? 


87. This property is possessed in an eminent degree by some oi 
the metals, especially gold, silver, iron and copper, and it is of vast 
importance in the arts. A knowledge of the uses of iron, and of its 
malleability, is one of the first steps from a savage to a civilized state 
of life. 

88. The most malleable of the metals is gold, which may be 
hammered to such a degree of thinness as to require three hundred 
and sixty thousand leaves to equal an inch in thickness.* 

89. Ductility. —Some substances admit of being extended simul¬ 
taneously both in length and breadth. Others can be extended to 
a greater degree in length alone ; and this property gives rise to 
another name, called Ductility. 


What is 90. Ductility. — Ductility is that property 
Ductility? which renders a- substance susceptible of being 
drawn out into wire. 


91. The same metals are not always both ductile and malleable 
to the same degree. Thus iron may be beaten into any form, when 
heated, but not into very thin plates, but it can be drawn into 
extremely fine wire. Tin and lead, on the contrary, cannot be drawn 
out into small wire, but they are susceptible of being beaten into 
extremely thin leaves. 

92. Gold and platinum have a high degree both of ductility and 
malleability. Gold can be beaten (as has already been stated) into 


permitted to cool very gradually, they will lose their brittleness anu 
icquire the opposite quality of flexibility. This process in the arts is 
Balled annealing. 

* The malleability of the metals varies according to their temper¬ 
ature. Iron is most malleable at a wTaite heat. Zinc becomes malleable at 
the temperature of 300^ or 400°. Some of the metals, and especially anti¬ 
mony, arsenic, bismuth and cobalt, possess scarcely any degree of this 
property. 

The familiar process of welding is dependent on malleability The two 
pieces of metal to be welded are first heated to that temperature at which 
y,hey are most malleable, and, the ends being placed together, the particles 
*re driven into such intimate connexicn by the welding-b nnmer that they 
cohere Different metals may in some eases be thus weldea together 


32 


NATURAL PHILOSOPHY. 


leaves so thin that it would require many thousands of them to equaj 
an inch in thickness. It has also been drawn into wife so atterm 
ated that one hundred and eight}' yards of it would not weigh more 
than a single grain. An ounce of such wire would f*e more thar 
fifty miles in length. But platinum can be drawn even to a fine.? 
wire than this. 

What is 93. Tenacitiy. — Tenacity implies, the adhesior 
'V.itfi ty? 0 f the particles of a body. 

94. Tenacity is one of the great elements of strength. It is th> 
absence of tenacity which constitutes brittleness. Both imply 
strength, but in different forms. Thus glass, the moct brittle of ah 
substances, has a great degree of tenacity. A slender tmI of glass, 
which cannot resist the slightest lateral pressure, ii suspended 
vertically by one end will sustain a very considerable weight at the 
other end.* 


* A knowledge of the tenacity of different substances ii* of great use in 
the arts. The tenacity of metals and other substances has ween ascertained 
oy suspending weights from wires of the metals, or rc^s and cords of 
iifferent materials. „ 

The following table presents very nearly the weights sjstained by wires 
of different metals, each having the diameter of about one-twelfth of an 
inch 


Lead, 

27 pounds. 

Silver, 

187 pounds. 

Tin, 

34 “ 

Platinum, 

274 « 

Zinc, 

109 “ 

Copper, 

302 « 

Gold, 

150 « 

Iron, 

549 « 


Cords of different materials, but of the same diameter, sustained the fol 
lowing weights : 

Common flax, 1175 pounds. New Zealand flax, 2380 pounds 

Hemp, 1633 “ Silk, 3400 “ 

The following table presents a more extended list of materials. The 
area of a transverse section of the rods on which the experiment was tried 
was one square inch. 


Pounds Avoirdupois. 


English Oak, 8,000 to 12,000 
Fir, 11,000 

Beech, 11,500 

Mahogany, 8,000 

Teak, 15,000 

Cast Steel, 134,256 

Iron Wire, 93,064 

Swedish Bar-iron, 72,064 

Cast-iron, 18,656 

Wrought Copper, 33,792 

Platinum Wire, 52,987 

Silver Wire, 38,257 

Hold, 30,888 

Zinc, 22,551 


Pounds Avoirdupois 

Tin, ' 

7,129 

Lead, 

3,146 

Rope, 1 inch in circum 

ference, 

1,000 

Whale line, 2 inches 

in 

circumference, spun 

by 

hand. 

2,240 

Do., by machinery, 

3,520 

Rope, 3 inches in circum- 

ference, 

5,628 

Do., 4 inches, 

9,988 

Cable, 14d inches. 

89,600 

Do., 23 iuches. 

‘255,360 


A more particular account el the tenacity of various substances will b* 


OF GRAVITY. 


95. The tenacity of metals is much increased by uniting them. 
A compound consisting of five parts of gold and one of copper nas a 
tenacity of more than double that of the gold or copper alone ; and 
brass, which is composed of copper and zinc, has a tenacity more 
than double that of the copper, and nearly twenty times as great as 
that of the zinc alone. A mixture of three parts of tin and one of 
load has a tenacity more than double that of the tin ; and a mixture 
of eight parts of lead and one of zinc has a tenacity nearly double 
that of the zinc, and nearly five times that of the lead alone.'* 

90 Gravity. —It has already been stated that matter in all its 
forms, whether solid, fluid or gaseous, possesses the property of 
attraction. This property, with its laws, is now to be particularly 
considered, under the name of Gravity. 

What is 97. Gravity is the reciprocal attraction of sep* 
Gravity? ara t e portions of matter. 

force do'all ^ bodies attract each other with a force pro- 
bodies at- portionate to their size, density and distance from 
1 other ea °h other. [iS'ee No. 59.] 

98. This law explains the reason why a body which is not sup 
ported falls to the earth. Two bodies existing in any portion of 
space mutually attract each other, and would rush together were 
they not preyented by some superior force. Let us suppose, for 
instance, that two balls made of the same materials, but one weigh¬ 
ing 11 pounds and the other weighing only one pound, were ten 
feet apart, but both were a hundred feet above the surface of the 
earth. According to this law, the two balls would rush together, 
the lighter ball passing over nine feet of the distance, and the 
heavier ball over one foot; and this they would do, were they not 
both prevented by a superior force. That superior force is the earth , 
which , being a much larger body, attracts them both with a superior force. 
This superior force they will both obey, and both will therefore fall 
to the earth. As the attraction of the earth and of the balls is 
mutual, the earth will also move towards the balls while the balls 
are falling to the earth ; but the size of the earth is so much greater 
than that of the balls, that' the distance that the earth would move 
towards the balls would be too small to be appreciated.! 


found in Barlow’s Essay on the Strength of Timber, Rennie’s Treatis* 
(in Phil. Trans. 1818), Tredgold’s Principles of Carpentry, and the 4th vol. 
of Manchester Memoirs, by Mr. Ilodgkinson. 

* There are many other specific properties of bodies besides those that 
have now been enumerate 1, the consideration of which belongs to th«. 
science of Chemistry. 

| The earth is one quatrillion, that is, ono thousand million miliionc 
times larger than the largest body which has ever been known to fal 


84 


KAVWJL PHILOSOPHY. 


99. The attraction o p -''.he earth is the cause of what we eafi 
weight. When we say that a body weighs an ounce, a pound, of 
a ton, we express by these terms the degree of attraction by which 
It is drawn towards the earth. Therefore, 


What is 100. Weight is the measure of the earth’s at- 
Weight ? traction.* 

101. As this attraction depends upon the quantity of matter 
which a body contains, it follows that 


What bodies 
have the 
greatest 
weight ? 


Those bodies will have the greatest weight 
which contain the greatest quantity of matter.f 


102. Terrestrial Gra^ -ty. — It has already been stated [see No. 
97 that the attraction wh ch one mass of matter lias for another is 
in proportion to the quantity and the distance; and that, the larger 
the quantity of matter ani the less its distance, the stronger will 
be the attraction. The law of this attraction may be stated as 
follows: 


What is the 103. Every portion of matter attracts every 
law of at- other portion of matter with a force proportioned 
directly to the quantity, and inversely as the 
square of the distance 


through our atmosphere. Supposing, then, tnat such a body should fall 
through a distance of one thousand feet, the earth would rise no more than 
the hundred billionth part of an inch, a distance altogether imperceptible 
to our senses. 

The principle of mutual attraction is not confined to the earth. It ex¬ 
tends to the sun, the planets, comets and stars. The earth attracts each 
of them, and each of them attracts the earth, and these mutual attractions 
aie so nicely balanced by the power of God as to cause the regular motions 
of all the heavenly bodies, the diversity of the seasons, the succession of 
day and night, summer and winter, and all the grand operations which are 
described in astronomy. 

* When we say that a body weighs an ounce, a pound, or a hundred 
pounds, we express, by these terms, the degree of attraction by which it is 
drawn towards the earth. 

t The weight of a htfdy is not dependent solely on its size or bulk ; its 
density must also be considered. If we take an equal quantity, by measure, 
of two substances, — lead and cork, for instance, — we shall find that, although 
both are of the same size, the lead will weigh much more than the cork. 
The Cork is more porous than the lead, and, consequently, the particles of 
which it is composed must be further apart, and therefore there must be 
fewer of them within a given bulk ; while, in the lead, the pores are much 
smaller, and the particles will, therefore, be crowded into a much amalle-i 
apace , 


OF GKAVITY. 


8 * 


104. Let us now apply this law to terrestrial gravity — that is, to 
the earth’s attraction; and, for that purpose, let us suppose four 
balls of the same size and density, to be placed respectively as fob 
lows, namely: 

The first at the centre of the earth. 

The second on the surface of the earth. 

The third above the earth’s surface, at twice the distance of the 
surface from the centre {that distance being four thousand miles) 

The fourth to be half way between the surface and the centre. 

To ascertain the attractive force of the earth on each of these balls, 
we reason thus: 

The first ball {at the centre) will be surrounded on all sides by an 
equal quantity of matter, and it will remain at rest. 

The second ball will be attracted downwards to the centre by the 
whole mass below it. 

The third ball, being at twice the distance from the surface (gravity 
decreasing as the square of the distance increases), will be attracted 
by a force equal to only one-fourth of that at the surface. 

The fourth ball, being attracted downwards by that portion of the 
earth which is below it, and upwards by that portion which is above 
it, will be influenced only by the difference between these two oppo¬ 
site attractions; and, as the downward attraction is twice as great as 
the upward, the downward attraction will prevail with half its 
original force, the other half being balanced by the upward attrac¬ 
tion. 

105. As weight is the measure of the earth's attraction , we may 
represent this principle by the weight of the balls, as follows {sup 
posing the weight of each ball , at the surface of the earth, to be one 
pound) : 

The first ball will weigh nothing. 

The second will weigh one pound. 

The third will weigh one-quarter of a pound. 

The fourth will weigh one-half of a pound. 

The law of terrestrial gravity, then, may be stated as follows 


What is the 
law of Ter¬ 
restrial 
Gravity ? 


106. The force of gravity is greatest at the sur¬ 
face of the earth, and it decreases upwards as the 
square of the distance from the centre increases, 
and downwards simply as the distance from the 


centre decreases. 


According to the principles just stated, a body which at the sur¬ 
face of the earth weighs a pound at the centre of the earth will 


weigh nothing. 

1000 rniks £ rom the centre it will 
2000 “ ‘ “ “ 

3000 “ ‘ “ “ 

4000 “ “ 44 “ 


weigh 1 of a pound 
“ £ of a pound. 

“ | of a pound 


1 pound. 


(t 




NATURAL PHILOSOPHY. 


8000 miles from the centre it will weigh ,1 of a pound. 

12000 “ 

tt tt 

a 

tt 

a 

4- 

1G000 “ 

tt tt 

tt 

a 

tt 

re* 

20000 “ 

it it 

tt 

tt 

tt 

sV 

24000 “ 

« <( 

tt 

tt 

tt 

3rV 

28000 “ 

a tt 

tt 

tt 

tt 

A- 

32000 “ 

tt tt 

tt 

tt 

tt 

eV 


If the principles that have now been stated have been understood, 
the solution of the following questions will not be difficult. 

107. Questions jor Solution. 

[N. B. We use the term weight in these questions in its philosophical 
sense, as “ the measure of the earth's attraction at the surface.”] 

(1.) Suppose that a body weighing 800 pounds could be sunk 500 
miles deep into the earth,—what would it weigh! 

Solution. 500 miles is | of 4000 miles ; and, as the distance from 
the centre is decreased by &, its weight would also be decreased in 
the same proportion, and the body would weigh 700 pounds. 

(2.) Suppose a body weighing 2 tons were sunk one mile below 
the surface of the earth, what would it weigh? Am. 1.9095 T. 

(3.) If a load of coal weighs six tons at the surface of the earth, 
what would it weigh in the mine from which it was taken, sup¬ 
posing the mine were at a perpendicular distance of half a mile 
from the surface? Am. 5.99925 T. 

(4.) If the fossil bones of an animal dug from a depth of 5228 feet 
from the surface, weigh four tons, what would be their weight at 
the depth where they were exhumed! Ans. ST. 19 cwt. 98 lb. + 

(5.) If a cubic yard of lead weigh 12 tons at the surface of the 
earth, what would it weigh at the distance of 1000 miles from the 
centre? Ans. 3 T. 

(6.) If a body on the surface of the earth weigh 4 tons, what would 
be its weight if it were elevated a thousand miles above the surface! 

Solution. Square the two distances 4000 and 5000, &c. 

Tons, cwt qrs. lbs. 

Answer. 2 11 0 20. 

(7.) Which will weigh the most, a body of 3000 tons at the dis¬ 
tance of 4 millions of miles from the earth, or a body of 4000 tons at 
the distance of 3 millions of miles! Ans. .003 T. and .007 T. + 

(8.) Ilow far above the surface of the earth must a pound weight 
be carried to make it weigh one ounce avoirdupois? Ans. 12000 mi. 

(9.) If a body weigh 2 tons wdien at tffi di ance of a thousand 
miles above the surface of'the eartn, whai ve Id it weigh at the 
surface! Ans. ST. Zcwt. hOlb. 

(10.) Suppose two balls ten thousand miles apart were to ap¬ 
proach each other under the influence of mutual attraction, the 
weight of one/being represented by 15, that of the other by 30 
Bow far would each move! Ans. G6G6§ mi. and 3333^ mi. 




OF GRAVITY 


37 


(11.) Which would have the stronger attraction on i ne earth, a body 
at the distance of 95 millions of miles from the earth, with a weight 
represented by 1000, or a body at the distance represented by 95, and 
a weight represented by one? Am. As 5 -„ 15 ff 4oooo« to mrs* 
( 12 .) Supposing the weight of a body to be represented by 4 ana 
its distance at (3, and the weight of another body to be 6 and its 
distance at 4, which would exert the stronger pow r er of attrac¬ 
tion ? Am. The second, as ^ to 5 . 


108. The Centre of Gravity. —As every part of a body possesses 
the general property of attraction, it is evident that the attractive 
force of the mass of a body must be concentrated in some point; and 
this point is called the centre of gravity of the body. 


What is the 
Centre of 
Gravity of a 
hody ? 


109. The Centre of Gravity of a body is the 
point about which, all the parts balance each 
other. 


110. This point in all spherical bodies ofUniform density will be 
the centre of sphericity. 

Ill As the earth is a spherical body, its centre of gravity is 
at the centre of its sphericity. 

112 . When bodies approach each other under the effect of mutual 
attraction, they tend mutually to approach the centre of gravity of 
each other. 

113. For this reason, when any body falls towards the earth its 
motion will be in a straight line towards the centre of the earth 
No two bodies from different points can approach 
the centre of a sphere in a parallel direction, and no 
two bodies suspended from different points can hang 
parallel to one another. 

114. Even a pair of scales hanging perpendicularly 
to the earth, as represented in Fig. 3, cannot be 
exactly parallel, because they both point to the same 
spot, namely, the centre of the earth. But their 
convergency is too small to be perceptible. 


Fig. 3. 



What is a 
Vertical 
Line 1 


115. The direction in which a falling body ap* 
proaches the surface of the earth is called a Vertical 
Line. 


No two vertical lines can be parallel. 


116. A weight suspended from any point will always assume a 
vertical position.* 


r Carpenters, masons and other artisans, make use of a weight of lead 
tsuepei.ded at rest by a string, for the purpose of ascertaining whether their 
work stands in a vertical position. To this implement they give the naru# 
of plumb -line, from the Lathi woH vtwnl vm, lead 

4 


88 


NATURAL PHILOSOPHY. 


117 All bodies under the influence of terrestrial gravity will fail 
to the surface of the earth in the same space of time, when at an 
equal distance from the earth, if nothing impede thern.^ But the 
air presents by its inertia a resistance to be overcome. This resist¬ 
ance can be more easily overcome by dei.se bodies, and therefore the 
rapidity of the fall of a body will be in proportion to its density. 


118. The resistance of the air to the fall of a 


To what is 
the resist¬ 
ance of the , . 

air to a fall- body is in direct proportion to the extent of its 

ing body sur face. 
propor¬ 
tioned 1 


119. Heavy bodies can be made to float in the air, instead of 
falling immediately to the ground, by making the extent of their 
surface counterbalance their weight. Thus gold, which is one of 
the heaviest of all substances, when spread out into thin leaf is not 
attracted by gravity with sufficient force to overcome the resistance 
of the air; it therefore floats in the air, or falls slowly. A sheet 
of paper also, for the same reason, will fall very slowly if spread 
open, but, if folded into a small compass, so as to present but a small 
surface to the air, it will fall much more rapidly. 

120. This principle will explain the reason why a person can 
with impunity leap from a greater height with an expanded um¬ 
brella in his hand. The resistance of the air to the broad surface 
of the umbrella checks the rapidity of the fall. 

121. In the same manner the aeronaut safely descends from a 
balloon at a great height by means of a parachute. But, if by any 
accident the parachute is not expanded as he falls, the rapidity of the 
*all will not be checked. [<See Fig. 4.] 

122. Effect of Gravity on the Density of the Air. — The air 
extends to a very considerable distance above the surface of the earth.* 
Chat portion which lies near the surface of the earth has to sustain 
she weight of the portions above ; and the pressure of the upper parts 

t 

* We have no means of ascertaining the exact height to which the air 
extends. Sir John Iierschel says: ‘‘Laying out of consideration all nice 
questions as to the probable existence of a definite limit to the atmosphere, 
beyond which there is, absolutely and rigorously speaking, no air, it is clear 
that, for all practical purposes, we may speak of those regions which are 
more distant above the earth’s surface than the hundredth part of its 
diameter as void of air, and, of course, of clouds (which are nothing but 
visible vapors, diffused and floating in the air, sustained by it, and render¬ 
ing it turhid, as mud does water). It seems probable, from many indica 
tions, that the greatest height at which visible clouds ever exist does noc 
exceed ten miles, at which height the density of the air is about an eighth 
part of what it is at the level of the sea.” Although the exact height to 
which the atmosphere extends has never been ascertained, it ceases t> 
feflec' the suu’s -a/s at a greater height than forty-five miles 


OF GRAVITY, 


39 

®{ the atmosphere on those beneath renders the air near the surface 
of the earth much more dense than that in the upper regions. 

Fig. 4. 



\Vhat eject 123. The air or atmosphere exists in a state 
ftcis Gi (ivity a • 1 i ^ • 

upon the °* compression, caused by Gravity, which in- 

air ? creases its density near the surface of the earth. 

124. Gravity causes bodies in a fluid or gaseous form to 
move in a direction seemingly at variance with its own laws. 

Thus smoke and steam ascend, and oil poured into a vessel con¬ 
taining a heavier fluid will first sink and then rise to the surface. 
This seemingly anomalous circumstance, when rightly understood 
will be found to be in perfect obedience to the laws of gravi¬ 
tation. Smoke and steam are both substances less dense than 
air, and are therefore less forcibly attracted by gravitation. 
The air being more strongly attracted than steam or smoke, on 
account of its superior density, falls into the space occupied by the 








NATURAL PIIILOSOPHI. 


4:0 


steam, anti forces it upwards. The same reasoning applies in tt» 
case of oil; it is forced upwards by the heavier fluid, and bot h pht> 
nomena are thus seen to be the necessary consequences of gravity. 
The rising of a cork or other similar light substances from the hot 
tom of a vessel of water is explained in the same way. This circum¬ 
stance leads to the consideration of what is called specific gravity 


What is 

meant by 
Specific 
Gravity ? 


125. Specific Gravity. — Specific Gravity 
is a term used to express the relative weight of 
equal bulks of different bodies.* 


126. If we take equal bulks of lead, wood, cork and air, we find 
the load to he the heaviest, then the wood, then the cork, and lastly 
the air. Ilence we say that the specific gravity of cork is greatei 
than that of air, the specific gravity of wood is greater than that of 
cork, and the specific gravity of lead greater than that of wuod, &e. 

127. From what has now been said with respect to the attrac 
tion of gravitation and the specific gravity of bodies, it appears that, 
although ;he earth attracts all substances, yet this very attraction 
Causes some bodies to rise and others to fall. 

128. Those bodies or substances the specific gravity of which 
is greater than that of air will fall, and those wdiose specific gravity 
is less than that of air will rise; or, rather, the air, being more 
strongly attracted, will get beneath them, and, thus displacing them 
will cause them to rise. 

For the same reason, cork 
and other light substances 
will not sink in water, be¬ 
cause, the specific gravity 
of water being greater, the 
water is more strongly at¬ 
tracted, and will be drawn 
down beneath them. [For 
a table of the specific 
gravity of bodies, see Hy¬ 
drostatics.] 

129. The principle which 
causes balloons to rise is 
the same which occasions 
the ascent of smoke, steam, 

. &c. The materials of which 



* The quantity of matter in a body is estimated, not by its apparent 
6 ize, but by its weight. Some bodies, as cork, feathers, &o., are termed 
light ; others, as lead, gold, mercury, <fcc., are called heavy. The reason 
of this is, that the particles which compose the former are nut closely 
packed together, and therefore they occupy considerable space ; while in 
the latter they are joined more closely together, and occupy but little room 
A pound of cork aud a pound of lead, therefore, will dilfer very much iu 
apparent size, while they are both equally attracted by the earth,— that i* 
they weigh the same 













MECHANICS. 


41 


a balloon is made, are heavier than air, but their extension is 
greatly increased, and they are filled with an elastic fluid of a dif 
ferent nature, specifically lighter than air, so that, on the whole, the 
balloon when thus filled is much lighter than a portion of air of the 
same dimensions, and it will rise. 

130. Gravity, therefore, causes bodies ■which are lighter than 
air to ascend, those which are of equal weight with air to remain 
stationary, and those which are heavier than air to descend. But 
the rapidity of their descent is affected by the resistance of the air, 
which resistance is proportioned to the extent of surface in the 
falling body. 

131. Mechanics. — Mechanics treats of mo- 
Mechanics ? ti° n ? and the moving powers, their nature and 
laws, with their effects in machines. 

li 'jtion? 1^2. ^°^ on a con tinued change of place. 


133. On account of the inertia of matter, a body at- rest cannot 
put itself in motion, nor can a body in motion stop itself 


What is 

meant by 134. That which causes motion is called a Force. 

c Force ? 


What is 
meant by 
Resist¬ 
ance ? 


135. That which stops or impedes motion is 
called Resistance.* 


What things 
are to be con¬ 
sidered in re¬ 
lation to mo¬ 
tion ? 


136. In relation to motion, we must consider 
the force, the resistance, the time, the space, 
the direction, the velocity and the momentum 


What is the The ve i oc ity is the rapidity with which a- 

velocity,and J 1 J 

o what is it body moves ; and it is always proportional to th* 
i proportion- f orce hy w hich the body is put in motion. 

138. The velocity of a moving body is determined by the time 
that it occupies in passing through a given space. The greater the 
space and the shorter the time, the greater is the velocity. Thus, 
if one body move at the rate of six miles, and another twelve miles 


* A force is sometimes a resistance, and a resistance is sometimes a force 
The t*v terms are used merely to den< t opposition. 

4 * 




NATURAL PHILOSOPHY 


42 


in the same time, the velocity of the latter is double that of tho 
former. 


What is 
the rule for 
finding the 
velocity of 
a moving 
body ! 


189. To find the velocity of a body, the space 
passed over must be divided by the time employed 
in moving over it. 


Thus, if a body move 100 miles in 20 hours, the velocity is found 
by dividing 100 by 20. The result is five miles an hour * 


140. Questions for Solution. 

(1.) If a body move 1000 miles in 20 days, what is its velocity I Amt. 
60 miles a day. 

(2.) If a horse travel 15 miles in an hour, what is his velocity 1 Am* 
i of a iniie in a minute. 

(3.) Suppose one man walk 300 miles in 10 days, and another 200 miles in 
the same time, — what are their respective velocities 1 Ans. 30 & 20. 

(4.) If a ball thrown from a cannon strike the ground at the distance of 
3 miles in 3 seconds from the time of its discharge, what is its velocity \ A. L, 

(5.) Suppose a flash of lightning come from a cloud 3 miles distant from 
the earth, and the thunder be heard in 14 seconds after the flash is seen; 
how fast does sound travel 1 Ans. 1131 ^ ft. per sec. 

( 0 .) The sun is 95 millions of miles from the earth, and it takes S$ 
minutes for the light from the sun to reach the earth ; with what velocity 
does light move 1 f Ans. 191919 -f- mi. per seo. 


* Velocity is sometimes called absolute, and sometimes relative. Veloe 
ity is called absolute when the motion of a body in space is considered 
without reference to that of other bodies. When, for instance, a horse goes 
a hundred miles in ten hours, his absolute velocity is ten miles an hour. 
Velocity is called relative when it is compared with that of another body. 
Thus, if one horse travel only fifty miles in ten hours, and another one 
hundred in the same time, the absolute velocity of the first horse is five 
miles an hour, and that of the latter is ten miles; but their relative velocity 
is as two to one. 

t From the table here subjoined, the velocities of the objects enumerated 
may be ascertained in miles per hour and in feet per second, fractions omitted 


TABLE OP VELOCITIES. 


Miles per hour. Feet per second. 

A man walking.3.4 

A horse trotting.7.10 

Swiftest race-horse . ..60 .88 

Railroad train in England .32. 47 

“ “ America .18.26 

“ “ Belgium .25.36 

** “ France 27 . . . . .40 

“ “ Germany 24. 35 

English steamboats in / , .. 

channels.$ 2b 


American on the Hudson . 18 
East-sailing vessels * . 10 


. 26 

14 


0 « • 














MECHANICS 


43 


Flow is the 
time employ¬ 
ed by a mov¬ 
ing body as¬ 
certained ? 


141. The time employed by a body in motion 
may be ascertained by dividing the space by the 
velocity. 


Thus, if the space passed over be 100 miles, and the velocity 5 mile* 
in an hour, the time will be 100 divided by 5. Ans. 20 hours. 


142. Questions for Solution. 

(1.) If a cannon-ball, with a velocity of 3 miles in a minute, strike the 
ground at the distance of one mile, what is the time employed I Ans. ± of 
a minute, or 29 seconds. 

(2.) Suppose light to move at the rate of 192,000 miles in a second of 
time, how long will it take to reach the earth from the sun, which is 95 
millions of miles distant ] Ans. 8 min. 14.07 sec. + 

(3.) If a railroad-car run at the rate of 20 miles an hour, how long will 
it take to go from Washington to Boston,—distance 432 miles'/ Ans. 21.6 hr. 

(4.) Suppose a ship sail at the rate of 6 miles an hour, how long will it 
take to go from the United States to Europe, across the Atlantic Ocean, a 
distance of 2800 miles 1 Ans. 19 da. 10 hr. 40 min. 

(5.) [f the earth go round the sun in 365 days, and the distance travelled 
be 540 millions of miles, how fast does it travel 1 Ans. 1.479.452 A m i. 

(6.) Suppose a carrier-pigeon, let loose at 6 o’clock in the morning from 
Washington, reach New Orleans at 6 o’clock at night, a distance of 1200 
miles, how fast does it fly 1 Ans. 100 mi. per hr. 

How may the 

svace passed ^43 The space passed over may be found by 
over by a body r 1 J J 

in motion be multiplying the velocity by the time. 
ascertained ? 


Miles per hour. 


Slow rivers. 

3 

Rapid rivers. 

7 

Moderate wind. 

7 

A storm. 

36 

A hurricane. 

80 

Common musket-ball ... 

850 





Air rushing into a vacuum ) 
at 32- E.S 

884 


Air gun bullet, air com- 5 
pressed to *01 of its > 

volume. . 

Sound . 

A point on the surface of ) 

the earth.5 

Earth in its orbit .... 


466 

743 

1,037 

67,374 




Feet per second. 

... 4 


10 

10 

52 

117 

1,240 


. . 1,466 
. . 2,346 


1,296 


683 

1,142 

1,520 

98,815. 


The vel.vity of light is 192,000 miles in a second of time. 

The velocity of the electric fluid is said to be still greater, and some 
authorities state it to be at the rate of 288 000 miles in a second of time. 























44 


NATURAL PHILOSOPHY. 


Thus, if the velocity be 5 miles an hour, and the time 20 hours 
the space will oe twenty multiplied by 5. Ans. 100 miles. 

144. (1.) If a vessel sail 125 miles in a day for ten days, how far will ii 

siil in that time ? A ns. 1250 mi. 

(2.) Suppose the average rate of steamers between New York and Albany 
be about il miles an hour, which they traverse in about 14 hours, what 
is the distance between these two cities by the river 1 Ans. 154 mi. 

(3.) Suppose the cars going over the railroad between these two cities 
travel at the rate of 25 miles an hour and take 8 hours to go over the dis¬ 
tance, how far is it from New York to Albany by railroad 1 Ans. 200 mi. 

(4.) If a man walking from Boston at the rate of 2 miles in an hour reach 
Salem in 6 hours, what is the distance from Boston to Salem 1 Ans. 15 mi. 

(5.) The waters of a certain river, moving at the rate of 4 feet in a 
second, reach the sea in (J days from the time of starting from the source 
of the river. What is the length of that river 1 Ans. S'J2 ~ mi. 

(0.) A cannon-ball, moving at the rate of 2400 feet in a second of time, 
strikes a target in 4 seconds. What is the distance of the target! .a. 9000 ft. 

145. The following formulae embrace the several ratios of the time, space 
and velocity : 

s 

(1.) The space divided by the time equals the velocity, or — = v * 

t 

8 

(2.) The space divided by the velocity equals the time, or — =. t. 

v 

(3.) The velocity multiplied by the time equals the space, or vXt = *. 

How many 

kinds of 146. There are three kinds of motion, namely, 

rno/ion are Uniform, Accelerated and Retarded. 
there f 


What is Uni- 147. Uniform Motion is that by which a 
form Motion ? body moves over equal spaces in equal times. 


What is Accel- 148. Accelerated Motion is that by which the 
traUd Motion l velocity increases while the body is moving. 


What is Re¬ 
tarded Mo¬ 
tion ? 


149. Retarded Motion is that by which the 
velocity decreases while the body is moving. 


How are uni¬ 
form i, accel¬ 
erated and re¬ 
ar did motion 
espectirely 
produced ? 


150. Uniform Motion is produced by the 
momentary action of a single force. Acceler¬ 
ated Motion is produced by the continued action 
of one or more forces. Retarded Motion is pro¬ 


duced by some resistance. 


151. A ball struck by a bat, or a stone thrown frcni the hand ie 


MECHANICS. 


45 


w theory an instance of uniform motion ; and, if the attraction of 
gravity and the resistance of the air could be suspended, it would 
proceed onwards in a straight line, with a uniform nation, forevr.:. 
But, as the resistance of the air and gravity both tend to deflect it, 
it in fact becomes first an instance of retarded, and then of accel¬ 
erated motion. 

152. A stone, or any other body, falling from a height, is an 
instance of accelerated motion. The force of gravity continues to 
operate upon it during the whole time of its descent, and con¬ 
stantly increases its velocity. It begins its descent with the first 
impulse of attraction, and, could the force of gravity which gave it 
the impulse be suspended, it would continue its descent with a 
uniform velocity. But, while falling it is every moment receiving a 
new impulse from gravity, and its velocity is constantly increasing 
during the whole time of its descent. 

153. A stone thrown perpendicularly upward is an instance of 
retarded motion ; for, as soon as it begins to ascend, gravity immedi¬ 
ately attracts it dowmvards, and thus its velocity is diminished. The 
retarding force of gravity acts upon it during every moment of its 
ascent, decreasing its velocity until its upward motion is entirely 
destroyed. It then begins to fall with a motion continually acceler¬ 
ated until it reaches the ground. 

What time 

floes a body 154. A body projected upwards will occupy the 

°ascent ! and same ^ me its ascent and descent. 

descent ? 

This is a necessary consequence of the effect of gravity, which 
uniformly retards it in the ascent and accelerates it in its descent. 

How can per- 155 Perpetual Motion. — Perpetual Mo- 
be produced? tion is deemed an impossibility in mechanics, 
because action and reaction are always equal and in con¬ 
trary directions. 

What is meant 150 j>„. the action of a body is meant the 
tty Action and J ^ 

Reaction ? effect which it produces upon another body. 

By reaction is meant the effect which it receives from the 

body on which it acts. 

Thus, when a body in motion strikes another body, it acts upon it, 
or produces motion ; but it also meets with resistance from the body 
which is struck, and this resistance is the reaction of the body. 


46 NATURAL PHILOSOPHY. 


Illustration of Action and Reaction by i leans of Elastic and 
Non-elastic Balls. 


(1.) Figure 6 represents two ivory * balls, A and B, Fig. 6. 
of equal size, weight, &c., suspended by threads. If the 
ball A be drawn a little on one side and then let go, 
it will strike against the other ball B. and drive it off A 
to a distance equal to that through which the first ball 
fell; but the motion of A will be stopped, because when it strikes 
B it receives in return a blow equal to that which it gave, but in 
a contrary direction, and its motion is thereby stopped, or, rather, 
given to B. Therefore, when a body strikes against another, 
the quantity of motion communicated to the second body is lost 
by the first; but this loss proceeds, not from the blow given by 
the striking body, but from the reaction of the body which it 
struck. 

(2.) Fig. 7 represents six ivory balls of equal weight, suspended 
by threads. If the ball A be drawn out. of the perpendicular 
and let fall against B. it will communicate its mo¬ 
tion to B, and receive a reaction from it which will 
stop its own motion. But the ball B cannot move 
without moving 0; it will therefore communicate 
the motion which it received from A to G. and 
receive from C a reaction, which will stop its motion. 

In like manner the motion and reaction are received by each oi 
the balls D, E, F; but, as there is m ball beyond F to act upon 
it, F will fiy off. 



A BCDE F 



Fig. 8. 


N. B. Thi« experiment is to be performed *vith elastic balls t I f. 

(3). Fig. 8 represents two bvlls of clay (which are rot elastic) 
of equal weight, suspended by swings. If the ball D 
be raised and let fall against E, only part of the mo¬ 
tion of 1) will be destroyed by it (because the bodies 
ai v nomelastic), and the two balls will move on togeth¬ 
er to and e , which are less distant from the ver¬ 
tical line than the ball I) was before it foil. Still, 



•It will be recollected that ivory is consider xt. lOrbly elastic 









MECHANICS. 


47 


itO^ovcr, action and reaction are equal, for the action cn K is 
onl) enough to make it move through a smaller space, but so 
much of D’s motion is now also destroyed.^ 

157. It is upon the principle of action and reaction that birds 
are enabled to dy. They strike the air with their wings, and the 
reaction of the air enables them to rise, fall, or remain stationary, 
at will, by increasing or diminishing the force of the stroke of theii 
wings, f 

158. It is likewise upon the same principle of action and reaction 
that fishes swim, or, rather, make their way through the water, 
namely, by striking the water with their fins. J 

159. Boats are also propelled by oars on the same principle, and 
the oars are lifted out of the water, after every stroke, so as com¬ 
pletely to prevent any reaction in a backward direction. 

How may 160 . Motion may be caused either by action o* 

caused ? reaction. When caused by action it is called 

Incident, and when caused by reaction it is called Rejected 

Motion. § 

* Figs. 6 and 7, as has been explained, show the effect of action ana re¬ 
action in elastic bodies, and Fig. 8 shows the same effect in non-elastic bodies. 
When the elasticity of a bojly is imperfect, an intermediate effect will bo 
produced ; that is, the ball which is struck will rise higher than in case of 
non-elastic bodies, and less so than in that of perfectly elastic bodies; and 
the striking ball will be retarded more than in the former case, but not 
stopped completely, as in the latter. They will, therefore, both move 
onwards after the blow, but not together, or to the same distance ; but . 
this, as in the preceding cases, the whole quantity of motion destroyed in 
the striking ball will be equal to that produced in the ball struck. Con¬ 
nected with “ the Boston school apparatus ” is a stand with ivory balls, to 
give a visible illustration of the effects of collision. 

f The muscular power of birds is much greater in proportion to their 
weight than that of man. If a man were furnished with wings sulliciently 
large to enable him to fly, he would not have sufficient strength or muscular 
power to put them in motion. 

\ Tho power possessed by fishes, of sinking or rising in the water, is 
greatly assisted by a peculiar apparatus furnished them by nature, called 
an air-bladder, by the expansion or contraction of which they rise or fall, 
ou the principle of specific gravity. 

§ The word incident implies Jailing upon, or directed towards. The word 
reflected implies turned back. Incident, nation is motion directed towards any 
particular object, against which a moving body strikes. Reflected motion 
is that which is caused by the reaction ot the body which is struck. Thus, 
when a ball is thrown against a surface, it rebounds or is turned back. This 
return of the ball is called reflected motion. As reflected motion is caused 
by reaction, and reaction is increased by elasticity, it follows that reflected 
motion is always greatest in those bodies which are most elastic. For tins' 
reason, a ball filled with air rebounds better than one stuffed with bran oi 
wool, because its elasticity is greater. For the same reason, balls made of 
caoutchouc, or India-rubber, will rebound mere than those which are mud 
" * must other aubstu aces- 




48 


NATURAL philosophy. 


What is 161. The angle * of incidence is the angle formed 
5 a jna- by the line which the incident body makes in its 
dtnte? passage towards any object, with a line perpendic¬ 
ular to the surface of the object. 


Fig. 9. 
R. 


* As this book may fall into the hands of some who are unacquainted with 
geometrical figures, a few explanations are here subjoined : 

1. An angle is the opening made by two lines which meet each other in a 
point. The size of the angle depends upon the opening , and not upon thi length 
of the lines. 

2. A circle is a perfectly round figure, every 
part of the outer edge of which, called the cir¬ 
cumference, is equally distant from a point 
within, called the centre. [See Fig. 9.] 

3. The straight lines drawn from the centre 
to the circumference are called radii. [The 
singular number of this word is radius.] Thus, 
in Fig. 9, the lines CD, C 0, C It, and C A, are 
radii. 

4. The lines drawn through the centre, and 
terminating in both ends at the circumference, 
are called diameters. Thus, in the same figure, D A is« diameter of the 
circle. 



C ' 


'A 


5. The circumference of all circles is divided into 3C0 equal parts, called 
degrees. The diameter of a circle divides the circumference into two equal 
parts, of 180 degrees each. 

6. All angles are measured by the number of degrees which the} T contain 
Thus, in Fig. 9, the angle R C A, as it includes one-quarter of the circle, is 
an angle of 90 degrees, which is a quarter of 300. And the angles KC 0 
and 0 0 D are angles of 45 degrees. 

T. Angles of 90 degrees are right angles ; angles of less than 90 degrees, 
acute angles; and angles of more than 90 degrees are called obtuse angles. 
Thus, in Fig. 9, ItC A i3 a right angle, 0 C R an acute, and 0 0 A an obtuse 
angle. 

8. A perpendicular line is a line which makes an angle of 90 degrees on 
each side of any other line or surface ; therefore, it will incline neither to 
the one side nor to the other. Thus, in Fig. 9, RC is perpendicular to D A. 

9. The tangent of a circle is a line which touches the circumference, with¬ 
out cutting it when lengthened at either end. Thus, in Fig. 9, the line RT 
is a tangent. 

10. A square is a figure having four equal sides, and four equal angles. 
These will always be right angles. [See Fig. 11.] 

11. A parallelogram is a figure whose opposite sides are equal and parallel 
[See Figs. 12 and 13.] A square is also a parallelogram. 

12 A rectangle is a parallelogram whose angles are right angles. 

[N. B. It will be seen by these definitions that both a square and a 
rectangle are parallelograms, but all parallelograms are not rectangles nor 
squares. A square is both a parallelogram and a rectangle. 'Three thing,* 
are. essential to a square; namely, the four sides must all be equal, they must 
ulso be parallel, and the angles must all be right angles. Two things only 
ure essential to a rectangle ; namely, the angles must all be right angles, 
and the opposite sides must be equal and parallel. One thing only is essen¬ 
tial to a parallelogram; namely, the opposite sides must be equal and 
parallel.] 

13 The diagonal of a square, t»f u paralle’ogram. or a rectangle, is a tin 





MECHANICS. 


4U 


Explain 
Mg. 10 


162. Thus, in Fig. 10, the line Fig. 10. 


ABC represents a wall, and P B 
a line perpendicular to its surface. 0 is a 
ball moving in the direction of the dotted 
ane, 0 B. The angle O B P is the angle of **' 
incidence. 

W hat. 163. The angle oi reflection is the angle formed 
of rcjlc- tbe perpendicular with the line made by the 
‘ ion? reflected body as it leaves the surface against 
which it struck. 

Thus, in Fig. 10, the angle P B B is the angle of reflection. 

What is the pro- ^ a . «... 

portion of the angle 104. Ihe angles of incidence and re- 

of incidence to the flection are always equal to one another.* 
angle of reflection? 

(1.) Thus, in Fig. 10, the angle of incidence, O B P, and the 
angle of reflection, P B B, are equal to one another; that is, 
they contain an equal number of degrees. 

165. From what has now been stated with 
regard to tho angles of incidence and reflec¬ 
tion, it follows, that when a ball is thrown 
perpendicularly against an object which 
it cannot penetrate , it will return in the same direction , 
but, if it be thrown obliquely , it will return obliquely on 
*lie opposite side of the perpendicular . The more ob¬ 
liquely the ball is thrown , the more obliquely it will 
rebound . f 

drawn through either of them, and terminating at the opposite angles. Thus, 
in Figs. 11, 12, and 13, the line A C is the diagonal of the square, parallelo¬ 
gram, or rectangle. 

* An understanding of this law of reflected motion is very important, 
because it is a fundamental law, not only in Mechanics, but also in Pyro- 
nomics, Acoustics and Optics. 

| It is from a knowledge of these facts that skill is acquired in many 
different sorts of games, as Billiards, Bagatelle, &o. A ball may also, on 
the same principle, be thrown from a gun against a fortification so as t© 
reach au object out of the range of a direct shot. 


What will he the 
course of a body 
in motion which 
strikes against 
anothet fixed 
■ iody ? 




50 


NATURAL PHILOSOPHY 


What is the 166. Momentum. — The Momentum * of a 
Momentum body is its quantity of motion, j* and it expresses 
oj a bouy ? p orce w iii C h. it would strike against 

another body. 

Momentum The Momentum of a body is ascertained b'j 

W a body multiplying its weight by its velocity. 
i ulculated ? 

167. Thus, if the velocity of a body be represented by 5 and its 

eight by 6, its momentum will be 30 

How can a 168. A small or a light body may be made 
h^Iit body to str ike against another body with a greater 
be made to force than a heavier body simply by giving it 
damage as sumcien; velocity,— that is, by making it have 
a large one 1 greater momentum. 

Thus, a cork weighing £ of an ounce, shot from a pistol with the 
velocity of 100 feet in a second, will do more damage than a leaden 
shot weighing J of an ounce, thrown from the hand with a velocity 
of 40 feet in a second, because the momentum of the cork will be 
the greater. 

The momentum of the cork is 1 X 100 = 25. 

That of the leaden shot is J X 40 =5 

169. Questions for Solution. 

1.) What is the momentum of a body weighing 5 pounds, moving with 

t velocity of 50 feet in a, second 1 Ans. 250. 

(2.) What is the momentum of a steam-engine, weighing 3 toms, moving 
v>ith the velocity of 60 miles in an hour 1 Ans. 180. 

[N. B. It must be recollected that, in comparing the momenta of bodies 
the velocities and the time of the bodies compared must be respectively of 
the same denomination. If the time of one be minutes and of the other be 
hours, they must both be considered in minutes, or both in hours. So. 
with regard to the spaces and the weights, if one be feet all must be 
expressed in feet ; if one be in pounds, all must be in pounds. It is better, 
however, to express the weight, velocities and spaces, by abstract numbers 
as follows :] 

(3.) If a body whose weight is expressed by 9 and velocity by 6 is in 
motion, what is its momentum 1 Ans. 54. 

(4.) A body whose momentum is 63 has a velocPy of 9; what is its weight 1 

Ans. 1 

* The plural of this word is momenta. * 

■f The quantity of motion communicated to a body does not affect the 
duration of the motion. If but little motion be communicated, the body 
will move slowly. If a great degree be imparted, it will move rapidly. 
But in both cases the motion will continue until it is destroyed by sums 
esfcerniii force 


MECHANICS. 


$4 


N 3. The momentum being the product of the weight and velocity, th« 
weight is found by dividing the momentum by the velocity, and the velocity 
is found by dividing the momentum by the weight.] 

(5.) The momentum is expressed by 12, the weight by 2 ; what is the 
yolocity ? A ns. 6. 

(6.) The momentum 9, velocity 9, what is the weight 1 An* 1. 

(7.) Momentum 3b, weight 6, required the velocity. Ann. 6. 

(8.) A body with a momentum of 12 strikes another with a momentum of 
6 ; what will be the consequence ] Am. Uotn have mom. ol'li. 

[N. B. VI hen two bodies, in opposite directions, come into collision, they each 
lose an equal quantity of their momenta .] 

(9.) A body weighing 16, with a velocitjk,of 12, meets another coming in 
the opposite direction, with a velocity of 20, and a weight of 10 ; what will 
he the etfect ? Am. Both move .vith mom. of 20. 

(10.) Two bodies meet together in opposite directions A has a velocity 
of 12 and a weight of 7, B has a momentum expressed by 84. What wib 
be the consequence 1 Am. Both morn, destroyed. 

(11.) Suppose the weight of a comet be represented by 1 and its velocity 
oy 12, and the weight of the earth be expressed by 100 and its velocity by 
10, what would be the consequence of a collision, supposing them to b< 
tuning in opposite directions ? An*. Botu have mom. of 988. 

(12.) If a body with a weight of 75 and a velocity of 4 run against a mui 
fihose weight is 150, and who is standing still, what will be the cons* 
quence, if the man uses no etiort but his weighty Am. Man has vel. of l.j. 

(13.) With what velocity must a 04 pound cannon-ball fly to be equally 
effective with a battering-ram of 12,000 pounds propelled with a velocity 
of 10 feet in a second \ • Am. 3000,/?. 

170. Attraction — Law of Falling Bodies. -—When one bod} 
strikes another it will cause an effect proportional to its own weight 
and velocity (or, in other words, its momentum) ; and the bodj 
which receives the blow will move on with a uniform velocity (if 
the blow be sufficient to overcome its inertia) in the direction of 
the motion of the blow. But, when a body moves by the force of 
a constant attraction, it will move with a constantly accelerated 
motion. 

171. This is especially the case with falling bodies. The earth 
attracts them with a ijrce sufficient to bring them down through a 
pertain number of feet during the first second of time. While the 
body is thus in motion with a velocity, say of sixteen feet, the earth 
still attracts it, ;md during the second second it communicates an 
additional velocity, and every successive second of time the attrac¬ 
tion of the earth adds to the velocity in a similar proportion, so that 
during any given time, a falling body will acquire a velocity which, 
in the same time, would carry it over twice the space through which 
it has already fallen. Hence we deduce the following law: 

What is the 172 . A body falling from a Leight will fall 
iny bodies? sixteen feet in the first second of time,* three 

* This is only an approximation to the truth ; it actually falls sixteen 
feet and one inch during the first second, three times that distance in th« 
second, The questions proposed to he solved assume sixteeu ftet oniv 


52 - 


natural PHILOSOPHY. 


times that distance in the second, five times in the 
third, seven in the fourth, its velocity increasing during 
every successive second, as the odd numbers 1, 3, 5, 7, 9 

n, is, & lg * 


The laws of falling bodies are clearly demonstrated by a mechanical 
arrangement known by the name of “ Attwood 's Mac hint in which a small 
weight is made to communicate motion to two others attached to a cord 
passing over friction-rollers (causing one to ascend and the other to 
descend), and marking the progress of the descending weight by the oscil¬ 
lations of a pendulum on a graduated scale, attached to one of the columns 
of the machine. It has not been deemed expedient to present a cut of the 
machine, because without the machine itself the explanation of its opera¬ 
tion would be unsatisfactory, with the machine itself in view the sim¬ 
plicity of its construction would render an explanation unnecessary. 

* The entire spaces through which a body will have fallen in any given 
number of seconds increase as the squares of the times. This law was dis¬ 
covered by Galileo, and may thus be explained. If a body fall sixteen feet 
in one second, in two seconds it will have fallen four times as far, in three 
seconds nine times as far, in four seconds sixteen times as far, in the fifth 
second twenty-five times, Ac., in the sixth thirty-six times, Ac. 


ANALYSIS OF THE MOTION OF A FALLING BODY. * 


Number of Seconds. 

Spaces. 

Velocities. 

Total Space 

1 

1 

2 

1 

2 

3 

4 

4 

3 

5 

6 

9 

4 

7 

8 

16 

5 

9 

10 

25 

6 

11 

12 

36 

7 

13 

14 

49 

8 

15 

16 

64- 

9 

17 

18 

8.1 

10 

19 

20 

100 

From this statement it appears that 

the spaces 

passed through by 

falling body, in any 

number of seconds. 

increase as 

the odd numbers 1, 


5, 7, i), 11, Ac. ; the velocity increases as the even numbers 2, 4, 6, 8, 10, 
12, Ac. ; and the total spaces passed through in any given number of 
seconds increase as the squares of the numbers indicating the seconds, 
— thus, 1, 4, 9, 16, 25, 3G, Ac. 

Aristotle maintained that the velocity of any falling body is in direct 
proportion to its weight; and that, if two bodies of unequal weight were let 
fall from any height at the same moment, the heavier body would reach the 
ground in a shorter time, in exact proportion as its weight exceeded that 
of the lighter one. Hence, according to his doctrine, a body weighing two 
pounds would fall in half the time required for the fall of a body weighing 
only one pound. This doctrine was embraced by all the followers of that 
distinguished philosopher, until the time of Galileo, of Florence, who flour¬ 
ished about the middle of the sixteenth century, lie maintained that the 
velocity of a falling body is not affected by its weight, and challenged the 
adherents of the Aristotelian doctrine to the test of experiment. The 
leaning tower of Pisa was selected for the trial, and there the experiment 
was tried which j roved the truth of Galileo’s theory. A distinguished 
writer thus describes the scene “ On the appointed day the disputant! 


MECHANICS. 


:y,y 

^73.^ The height of o, building, or the depth of a well, may thus 
be estimated very nearly by observing the length of time which s 
stone takes in falling from the top to the bottom. 


174. Exercises for Solution. 

(1.) If a ball, dropped lrom the top of a steeple, reaches the ground in 5 
seconds, how high is that steeple 1 

l(>-j-48-j-S0-|-l] 2—|— 144=400 feet ; or, 5X5=25, square of the number 
of seconds, multiplied by the number of feet it falls through in one second, 
namely, 10 feet ; that is, 25X16=^40(1 feet. 

(2.) Suppose a ball, dropped from the spire of a cathedral, reach the 
ground in 9 seconds, how high is that spire ? 

|—tS—j—80—|—112—j—144—j—17C»—j—208—j—240—(—272=1296 feet. 

Or, squaring the time in seconds, 9^=81, multiplied by 16=1:26. Ans. 

[It will hereafter be shown that this law of falling bodies applies to all 
bodies, whether falling perpendicularly or obliquely. Thus, whether a 
stone be thrown from the top of a building horizontally or dropped perpen¬ 
dicularly downwards, in both cases the stone.will reach the ground in the 
same time ; and this rule applies equally to a ball projected from a cannon, 
and to a stone thrown from the baud.] 

(3 ) If a ball, projected from a cannon from the top of a pyramid, reach 
the ground in 4 seconds, how high is the pyramid 1 Ans. 256 ft. 

(4.) How deep is a well, into which a stone being dropped, it reaches the 
water 6 feet from the bottom of the well in 2 seconds 1 Ana. 70 ft. 

(5.) The light of a meteor bursting in the air is seen, and in 45 seconds 
a meteoric stone falls to the ground. Supposing the stone to have pro¬ 
ceeded from the explosion of the meteor perpendicularly, how far from 
the earth, in feet, was the meteor 1 45 2 X16—=32,400 feet. 

(6.) W hat is the difference in the depth of two wells, into one of which a 
stone being dropped, is heard to strike the water in 5 seconds, and into 
the other in 9 seconds, supposing that the water be of equal depth in both, 
and making no allowance for the progressive motion of sound 1 A. S96./15. 


repaired to the tower of Pisa, each party, perhaps, with equal confidence. 
It was a crisis in the history of human knowledge. On the one side stood 
the assembled wisdom of the universities, revered for age and science, 
venerable, dignified, united and commanding. Around them thronged the 
multitude, and about them clustered the associations of centuries. On the 
other there stood an obscure young man (Oalileo), with no retinue of fol¬ 
lowers, without reputation, or influence, or station. But his courage was 
equal to the occasion ; confident in the power of truth, his form is erect 
and his eye sparkles with excitement. But the hour of trial arrives. The 
balls to be employed in the experiments are carefully weighed and scru 
tinized, to detect deception. The parties are satisfied. The one ball is 
exactly twice the weight of the other. The followers of Aristotle maintain 
that, when the balls are dropped from the tower, the heavy one will reach 
the ground in exactly half the time employed by the lighter ball. Galilee 
asserts that the weights of the balls do not affect their velocities, and that 
the times of descent will be equal ; and here the disputants join issue 
The balls are conveyed to the summit of the lofty tower. The crowd as 
somble round the base ; the signal is given ; the balls are dropped at the 
same instant ; and, swift descending, at the same moment they strike the 
earth. Again and again the experiment is repeated, with uniform results 
Galileo’s triumph was complete ; not * 3hadow of a doubt remained ‘ 

[ !< [i'he Orbs uj Heaven.'’] 


54 


NATURAL PHiLOSOx'JlY. 


(7.) A boy raised his kioe in the night, with a lantern attached to it 
l T nf( 'uunately, the string which attached the lantern broke, and the lantern 
fell U. the ground in 6 seconds. How high was the kite l Ans. 576/k 

175. Retarded Motion of Bodies Projected Upwards. —All the 
circumstances attending the accelerated descent of falling bodies are 
exhibited when a body is projected upwards, but in a reversed order. 


Ilow can we 17 G. To ( t e t crm i ne the height to which a 

determine the # ° 

height to which body, projected upwards, will rise, with a 

a body, pro- ve n velocity, it is only necessary to deter- 
jeeted upwards ° . , . J 

with a given mine the height from which a body would fall 

velocity, will aC q U j re the same velocity- 
ascend ? 1 J 


177. Thus, if it be required to ascertain how high a body would 
rise when projected upwards with a force sufficient to carry it it** 
feet in the first second of time, we reverse the series of numbers 
10 —(— 48 —|— 80-4- 112—J- 144 [ see table on page 52], and, reading 
them backward, 144 -j- 112 -4-80-J- 48 10, we find their sum to be 
400 feet, and the time employed would be 5 seconds. 

How does the 

time of the as- 178. The time employed in the ascent and 

cent oj a body d escen t of a body projected upwards will, 
compare with J r ° 1 

the time of its therefore, always be equal. 
descent 2 

Questions for Solution 

(1.) Suppose a cannon-ball, projected perpendicularly upwards, returned 
to the ground in 18 seconds ; how high did it ascend, and what is the velocity 
of projection ? Ann 1'2i Wft.; ‘27‘2/t. 1 st see. 

(2.) llow high will a stone rise which a man throws upward with a force 
sufficient to carry it 48 feet during the first second of time 1 Ann. 64 Ji. 

(8.) Suppose a rocket to ascend with a velocity sufficient to carry it 176 
feet during the first second of time ; how high will it ascend, and what 
time will it occupy in its ascent and descent I A ns. 576y?.: 12 see. 

(4.) A musket-ball is thrown upwards until it reaches the height of 400 
feet. Ilow long a time, in seconds, will it occupy in its ascent and descent, 
and what space does it ascend in the first second? Ann. 10 see. ; 144 ft. 

(5.) A sportsman shoots a bird flying in the air, and the bird is 3 
seconds in falling to the ground. How high up was the bird when he was 
shot ? Ans. 144 ft. 

(6 ) ITow ljrig time, in seconds, would it take a ball to reach an object 
5000 feet above the surface of the earth, provided that the ball be projected 
with a force sufficient only to reach the object 1 Ans. 17.67 see. -f- 


179. Compound Motion. — Motion may be produced 
either by a single force or by the operation of two or more 
lomea 


MECHANICS. 


5ft 


hi what direc- 180. Simple Motion, is tlie motion of a body 
Zl im P elled b y a force, and is always in a 

impelled by a straight line in the same direction with the 
single force? force that acts. 


What is Com- 181. Compound Motion is caused by the 
pound Motion? O p era tion of two or more forces at the same 
time. 

When a body 

is struck by two 182. When a body is struck by two equal 
Opposite direc- f° rces > °PP°site directions, it will remain at 
tions, how will rest. 
it move ? 


183. If the forces be unequal , the body ■will move with dimin¬ 
ished force in the direction of the greater force. Thus, if a body 
with a momentum of 9 be opposed by another body with a momen¬ 
tum of 6, both will move with a momentum of 3 in the direction of 
the greater force. 

How will a 184. A body, struck by two forces in dif- 
body move ferent directions, will move in a line between 
^twTfwces^m them, in the direction of the diagonal of a 
different direc- parallelogram, having for its sides the lines 
through which the body would pass if urged . 
by each of the forces separately. 

How will the 

body move , if 185. When the forces are equal and at 
ri S ht an o les t0 eacb other > tbe bo(l y Will 

right angles to move in the diagonal of a square, 
each other ? 


186. Let Fig. 11 represent a ball struck by 
the two equal forces X and Y. In this figure 
the forces are inclined to each other at an angle 
of 90°, or a right angle. Suppose that the 
force X would send it from C to B, and the 
force Y from C to D. As it cannot obey both, 
it will go between them to A, and the line C A, 


Fig. 11. 

x 

D C 




50 


NATUHAL PHILOSOPHY. 


through which it passes, is the diagonal of the square, A L C b 
This line also represents the resultant of the two forces. 

The time occupied in its passage from C to A will be the 
same as the force X would require to send it to B, or tne force 
Y to send it to I). 


fody move 187. If two unequal forces act at right 
under the influ- angles to each other on a body, the body will 
Tqualforce^at move i n the direction of the diagonal of a 


right angles to rectangle . 
each other. ? 


each other,i 

Explain Fig. 188. Illustration. — In Fig. 12 
12. represented as acted upon by 

two unequal forces, X and Y. The force X 
would send it to B, and the force Y to D. As 
it cannot obey both, it will move in the direc¬ 
tion C A, the diagonal of the rectangle A B G D. 


the ball C 

Fig. 12. 



How will the body move 
if the forces act in the 
direction of any other 
than a right angle? 
Hoio will a body move if 
the forces act in the di¬ 
rection of an acute or 
obtuse angle? 


189. When two force*. zjqI in the 
direction of an acute o/ an obtuse 
angle, the body will rsm in the di¬ 
rection of the diagonal of a parallelo¬ 
gram. 


Explain 190. Illustration. — In figure lo the ball C is 
Fig. 13. supposed to be influenced by two Flg> 13< 

forces, one of which would send it to B and 
the other to D, the forces acting in the 
direction of an acute angle. The ball will, 
therefore, move between them in the line 
G A, the longer diagonal of the parallelogram A B C D. 

191. The same figure explains the motion of a ball when the 
two forces act in the direction of an obtuse angle. 



192. Illustration. — The ball D, ui.der the influence of twt 







MECHANICS. 


57 


forces, one of which would send it to C, and the other to A, 
which, it will be observed, is in the direction of an obtuse 
angle, will proceed in this case to B, the shorter diagonal of the 
parallelogram ABCD. 


[N. B. A parallelogram containing acute and obtuse angles has tw* 
diagonals, the one which joins the acute angles being the longer.] 


What is Re¬ 
sultant Mo¬ 
tion ? 


193. Resultant Motion is the effect or re 
suit of two motions compounded into one. 


194. If two men be sailing in separate boats, in the same 
. direction, and at the same rate, and one toss an apple to the 
other, the apple would appear to pass directly across from one 
to the other, in a line of direction perpendicular to the side of 
each boat. But its real course is through the air in the diag¬ 
onal of a parallelogram, formed by the lines representing the 
course of each boat, and perpendiculars drawn to those lines 
from the spot where each man stands as the one tosses and the 
Explain other catches the apple. In Fig. 14 ^ ^ 

Fig. 14. the lines A B and C D represent the G F 

course of each boat. E the spot where the man A ~ 7 B 

stands who tosses the apple ; while the apple is c ^ ^ D 

in its passage, the boats have passed from E 
and G to II and F respectively. But the apple, having a 
motion, with the man, that would carry it from E to H, and 
likewise a projectile force which would carry it from E to G, 
cannot obey them both, but will pass through the dotted line 
E F, which is the diagonal of the parallelogram E G F H.* 


How can we 
ascertain the 
direction of the 


195. When a body is acted upon by three o^ 
more forces at the same time, we may take any 


* On the principle of resultant motion, if two ships in an engagement be 
eailino- before the wind, at equal rates, the aim of the gunners will be 
exactly as though they both stood still. But, if the gunner fire from a ship 
standing still at another under sail, or a sportsman fire at a bird on the 
vrin ir , each should take his aim a little forward of the mark, because the 
snip and the bird will pass a little forward while the shot is passing to 
them. 






58 


NATURAL PHILOSOPHY. 


motion when two of them alone, and ascertain the resultant of 

he body is in* ^ 10ge t wo anc [ t } ien eni p] 0 y the resultant as a nevt 
7 uenced by } J 

hree or more force, in conjunction with the third,* &c. 
f orces ? 

What is Cir- 196. Circular Motion. — Circular Mo- 
cular Motion ? tion is motion around a central point. 

_ 19T. Circular motion is caused by the con- 

n hat causes J 

Circular Mo- tinued operation of two forces, by one of which 

ticn! the body is projected forward in a straight 

line, while the other is constantly deflecting it towards a 

fixed point. [See No. 184.] 


198. The whirling of a ball, fastened to a string held by the 
hand, is an instance of circular motion. The ball is urged by two 
forces, of which one is the force of projection, and the other the 
string which confines it to the hand. The two forces act at right 
angles to each other, and (according to No. 18 ±) the ball will move 
in the diagonal of a parallelogram. But, as the force which con¬ 
fines it to the hand only keeps it within a certain distance, without 
drawing it nearer to the hand, the motion of the ball will be through 
the diagonals of an indefinite number of minute parallelograms, 
formed by every part of the circumference of the circle. 


How many 199. There are three different centres which 

centres re- require to be distinctly noticed ; namely, the 

(pare to be . , 7 

noticed in Me- Centre ot Magnitude, the Centre of Gravity, 

chanics / and the Centre of Motion. 


* The resultant of two forces is always described by the third side of a 
triangle, of which the two forces may be represented, in quantity and 
direction, by the other two sides. When three forces act in the direction 
of the three sides of the same triangle, the body will remain at rest. 

When two forces act at right angles, the resultant will form the hypothe 
nuse of a right-angled triangle, either of the sides of which may be found, 
when the two others are given, by the common principles of arithmetic or 
geometry. 

From what has now been stated, it will easily be seen, that if any number 
of firces whatever act upon a body, and in any directions whatever, the 
resultant of them all may easily be found, and this resultant will be their 
mechanical equivalent. Thus, suppose a body be acted upon at the same 
time by six forces, represented by the letters A, B, 0, D, E, F. First find 
the resultant ol A and li by the law stated in No. 1S4, and call this resultant 
<4. In the same, manner, find the resultant of G and C, calling it 11. Then 
find the resultant of II and 1), and thus continue until each of the forces be 
found, and the last resultant will be the mechanical equivalent of the whole 





MECHANICS. 


50 


\\hd i 2 s the 200. The Centre of Magnitude is the central 

Centre of , ° 

Magnitude, P 0 ^ of the bulk of a body. 


What is the 
Centre of 
Gravity ? 


201. The Centre of Gravity is the point 
about which all the parts balance each other. 


What is the 
Centre of 
Motion? 


202. The Centre of Motion is the point 
around which all the parts of a body move. 


What is the 
Axis of Mo¬ 
tion ? 

called the 


203. When the body is not of a size nor 
shape to allow every point to revolve in the 
same plane, the line around which it revolves 
Axis of Motion.* 


Does the cen¬ 
tre or the axis 
■f motion re¬ 
vive ? 


204. The centre or the axis of motion is 
generally supposed to be at rest. 


205. Thus the axis of a spinning-top is stationary, while every 
other part is in motion around it. The axis of motion and the 
centre of motim are terms which relate only to circular motion. 


What are Cen- 206. The two forces by wliich circular 
tral Forces? motion is produced are called Central Forces. 
Their names are, the Centripetal Force and the Centrifugal 
Force, f 


What is the 
Centripetal 
Force ? 


207. The Centripetal Force is that which 
confines a body to the centre around which it 
revolves. 


What is the 
Centrifugal 
Force ? 


208. The Centrifugal Force is that which 
impels the body to fly off from the centre. 


* Circles may have a centre of motion ; spheres or globes have an axie 
of motion. Bodies that have only length and breadth may revolve around 
their own centre, or around axes ; those that have the three dimensions of 
length, breadth and thickness, must revolve around axes. 

f The word centripetal means seeking the centre, and cenHfugal means 
flying from the centre. In circular motion these two forces constantly 
balance each other ; otherwise the revolving body will either "7 prua?h 
the centre, or recede from it, according as the centripetal or centrifuga/ 
force is the stronger. 


60 


NATURAL PHILOSOPHY. 


What follows 209. If the centrifugal force of a revolving 

if the ccntri V~ body be destroyed, the body will immediately 
etal or cen- J J „ 

trifugalforce approach the centre which attracts it; but it 

be destroyed? the centripetal force be destroyed, the body 

will fly off in the direction of a tangent to the curve which 

it describes in its motion.* 

210. Thus, when a mop filled with water is turned swiftly round 
by the handle, the threads which compose the head will fly off from 
the centre; but, being confined to it at one end, they cannot part from 
it; while the water they contain, being unconfined, is thrown off 
in straight lines. 


is 7 revolving 211. The parts of a body which are furthest 

around its from the centre of motion move with the 
centre or its greatest velocity ; and the velocity of all the 

parts move with parts diminishes as their distance from the 

the greatest ax j 3 0 f mo tion diminishes. 
velocity ? 


Explain 212. Fig. 15 represents the vanes of a windmill. 
Fig. 15. The circles denote the paths in which the different 
parts of the vanes move. M is the centre Fig i6 

or axis of motion around which all the 
parts revolve. The outer part revolves in 
the circle DEFG, another part revolves 
in the circle H IJ K, and the inner part in v 
the circle L N 0 P. Consequently, as they 
all revolve around M in the same time, the 
velocity of the parts which revolve in the 
outer circle is as much greater than the velocity of the parts 
which revolve in the inner circle, L N 0 P, as the diameter of 
the outer circle is greater than the diameter of the inner. 



* The centrifugal force is proportioned to the square of the velocity of a 
moving body. Hence, a cord sufficiently strong to hold a heavy body 
revolving around a fixed centre at the rato of fifty feet in a second, would 
require to have ics strength increased four-fold, to hold the same ball, if it* 
velocity should be doubled. 


MECHANICS. 


6*1 


In the daily revolu- 213. As the earth revolves round its 
iion of the earth . 

around its own axis , ^ lollows, from the preceding iiius- 

what parts of the tration, that the portions of the earth 
earth move /aost . 1 

slowly, and what which move most rapidly are nearest to the 
parts most rapidly ? equator, and that the nearer any portion 
of the earth is to the poles the slower will be its motion. 


What is re¬ 
quired in order 
to produce 
curvilinear 
motion l and 
why ? 


214. Curvilinear motion requires the action 
of two forces; for the impulse of one single 
force always produces motion in a straight 
line. 


What effect 215. A body revolving rapidlv around its 

tias the ceixtri]- ” l •/ 

ugal. force on l ori g er axis, if suspended freely, will gradually 

a body revolt- change the direction of its motion, and revolve 
longer axis l around its shorter axis. 


This is due to the centrifugal force, which, impelling the parts 
from the centre of motion, causes the most distant parts to revolve 
in a larger circle.* 


* This law is beautifully illustrated by a simple apparatus, in which a 
hook is made to revolve rapidly by means of multiplying wheels. Let an 
oblate spheroid, a double cone, or any other solid having unequal axes, be 
suspended from the hook by means of a flexible cord attached to the ex¬ 
tremity of the longer axis. If, now, it be caused rapidly to revolve, it will 
immediately change its axis of motion, and revolve around the shorter axis. 

The experiment will be doubly interesting if an endless chain be sus¬ 
pended from the hook, instead of a spheroid. So soon as the hook with the 
chain suspended is caused to revolve, the sides of the chain are thrown out¬ 
ward by the centrifugal force, until a complete ring is formed, and then the 
circular chain will commence revolving horizontally. This is a beautiful 
illustration of the effects of the centrifugal force. An apparatus, with a 
?hain and six bodies of different form, prepared to be attached to the multi¬ 
plying wheels in the manner described, accompanies most sets of philo¬ 
sophical apparatus. 

Attached to the same apparatus is a thin hoop of brass, prepared for con 
nexion with the multiplying wheels. The hoop is made rapidly to revolve 
around a vertical axis, loose at the top and secured below. So soon as the 
Loop begins to revolve rapidly, the horizontal diameter of the ring begins 
to increase and the vertical diameter to diminish, thus exhibiting the 
manner in which the equatorial diameter of a revolving body is lengthened, 
and the polar diameter is shortened, by reason of the centrifugal force. 
The daily revolution of the earth around its axis has produced this effect. 
So that the equatorial diameter is at least twenty-six miles longer than the 
pular. In those planets that revolve faster than the earth the effect is still 

b 


NATURAL PHILOSOPHY. 


62 


What is Pro- 216. Projectiles. — Projectiles is a trancT 
jectiles . Mechanics which treats of the motion of 

bodies thrown or driven by an impelling force above the 
surface of the earth. 

What is a 217. A Projectile is a body thrown into the 
Projectile ? a ir,— as a r0 eket, a ball from a gun, or a 
stone from the hand. 


„ The iorce of gravity and the resistance of the 

How are pro - . . . _ . . . . . 

jectiles affected air cause projectiles to lorui a curve both in their 

ir. their mo- ascent and descent; and, in descending, their 

motion is gradually changed from an oblique 

towards a perpendicular direction. 


Explain 218. In Fig. 16 the force of projection would carri* 
Fig. 16. a ball from A to D, while gravity would bring it h 
C. If these two forces alone prevailed, the Ficr J6 

bad would proceed in the dotted line to B. D A 

But, as the resistance of the air operates in 
direct opposition to the force of projection, 
instead of reaching the ground at B, the ball b — 
will fall somewhere about E.^ 


Fig. 16. 



What is the 
course of a 
body thrown 
obliquely in a 
horizontal 
direction ? 


219. When a body is thrown 
in a horizontal direction, or up¬ 
wards or downwards, obliquely , its 
course will be in the direction of 
a curve-line, called a parabola t 


Fig. 17. 



more striking, as is the case with the planet Jupiter, whose figure is nearlj 
that of an oblate spheroid. 

The developments of Geology have led some writers to the theory that 
the earth, during one period of its history, must have had a different axi; 
of motion ; but it will be exceedingly difficult to reconcile such a theory i 
the law of rotations which has now been explained, especially as a mu< v 
more rational explanation can be given to the phenomena on which the 
Iheoiy was built. 

* It is calculated that the resistance of the air to a cannon-ball of tw« 
pounds’ weight, with the velocity of two thousand feet in a second, is moi« 
lhan equivalent to sixty times the weight of the ball. 

t The science of gunnery is founded upon the laws relating to projectile* 






MECHANICS. 


08 

(see Fig. 17) ; but when it is thrown perpendicularly upwards 
or downwai Is, it will move perpendicularly, because the force 
of projection and that of gravity are in the same line of 
direction. 

The force of gunpowder is accurately ascertained, and calculations are 
predicated upon these principles, which enable the engineer to direct hia 
guns in such a manner as to cause the fall of the shot or shells in the very 
spot where he intends. The knowledge of this science saves an immense 
expenditure of ammunition, which would otherwise be idly wasted, without 
producing any effect. In attacks upon towns and fortifications, the skilful 
engineer knows the means he has in his power, and can calculate, with 
great precision, their effects. It is in this way that the art of war has been 
elevated into a science, and much is made to depend upon skill which, 
previous to the knowledge of these principles, depended entirely upon 
physical power. 

The force with which balls are thrown by gunpowder is measured by an 
instrument called the Ballistic pendulum . It consists of a large block of 
wood, suspended by a rod in the manner of a pendulum. Into this block 
tho balls are fired, and to it they communicate their own motion. Now, 
the weight of the block and that of the ball being known, and the motion 
or velocity of the block being determined by machinery or by observation, 
the elements are obtained by which the velocity of the ball may be found ; 
for the weight of the ball is to the weight of the block as the velocity of the block is 
to the velocity of the. ball. By this simple apparatus many facts relative to 
the art of gunnery may be ascertained. If the ball be fired from the same 
gun, at different distances, it will be seen how much resistance the atmo¬ 
sphere opposes to its force at such distances. Rifles and guns of smooth 
bores may be tested, as well as the various charges of powder best adapted 
to different distances and different guns. These, and a great variety of 
other experiments, useful to the practical gunner or sportsman, may be 
made by this simple means. 

The velocity of balls impelled by gunpowder from a musket with a 
sommon charge has been estimated at about 1050 feet in a second of time, 
when first discharged. The utmost velocity that can be given to a cannon¬ 
ball is 2000 feet per second, and this only at the moment of its leaving tae 
gun. 

In order to increase the velocity from 1650 to 2000 feet, one-half more 
powder is required ; and even then, at a long shot, no advantage is gained, 
since, at the distance of 500 yai’ds k the greatest velocity that can be ob¬ 
tained is only 1200 or 1300 feet per second. Great charges of powder are, 
therefore, not only useless, but dangerous ; for, though they give little 
additional force to the ball, they hazard the lives of many by their liability 
to burst the gun. 

Experiment has also shown that, although long guns give a greater 
velocity to the shot than short ones, still that, on the whole, short ones are 
preferable ; and, accordingly, armed ships are now almost invariably 
furnished with short guns, called carronades. 

The length of sporting guns has also been greatly reduced of late yeais 
Formerly, the barrels were from four to six feet in length ; but the best 
fowling-pieces of the present day have barrels of two feet or two and a half 
only in length Guns of about this length are now universally employed 
for such game as woodcocks, partridges, grouse, and such birds as are taken 
on the wing, with the exceptions of ducks and wild geese, which require 
louge f and heavier guns 


64 


NATURAL PHILOSOPHY. 


IV7u2/ forces 220. A ball thrown in a hoi zontal direction 
ajject a hor- 

izontal -pro - is influenced by three forces ; namely, first, the 
whatejject^do ^ orce puojeGtion (which gives it a horizontal 
they produce? direction) ; .second, the resistance of the air 
through which it passes, which diminishes its velocity, with¬ 
out changing its direction; and third, the force of gravity j 
which finally brings it to the ground. 


How is the 
force of 
gravity af¬ 
fected hy the 
f rce of pro¬ 
jection, ' 


221. The force of gravity is neither increased 
nor diminished by the force of projection.* 




V 5 


iiu2 


\ 6 


Explain 222. Fig. 18 represents a Fi g- 18 

18. cann0I1) loaded with a ball, 
and placed on the top of a tower, at 
such a height as to require just three 
seconds for another ball to descend per¬ 
pendicularly. Now, suppose the can¬ 
non to be fired in a horizontal direc¬ 
tion, and at the same instant the other balhto be dropped towards 
the ground. They will both reach the horizontal line at the 
base of the tower at the same instant. In this figure G 
a represents the perpendicular line of the falling ball. C h is 
the curvilinear path of the projected ball, 3 the horizontal line 
xt the base of the tower. During the first second of time, the 
'ailing ball reaches 1, the next second 2, and at the end of the 


* The action of gravity being always the same, the shape of the curve of 
every projectile depends on the velocity of its motion ; but, whatever this 
velocity.be, the moving body, if thrown horizontally from the same eleva¬ 
tion, will reach the ground at the same instant. Thus, a ball from a cannon, 
with a charge sufficient, to throw it half a mile, will reach the ground at the 
same instant of time that it would had the charge been sufficient to throw it 
one, two, or six miles, from the same elevation. The distance to which a 
ball will be projected will depend entirely on the force with which it is 
thrown, or on the velocity of its motion. If it moves slowly, the distance 
will be short ; if more rapidly, the space passed over in the same time 
will be greater ; but in both cases tie descent of the ball towards the earth 
in the same time, will be the same number of feet, whether it mi. res fast o» 
slow, or even whether it move forward at all. or not. 













MECHANICS. 


65 


<&ird second it strikes the ground. Meantime, that projected 
from the cannon moves forward with such velocity as to reach 
4 at the same time that the falling ball reaches 1. But the 
projected ball falls downwards exactly as fast as the other, since 
it meets the line 1 4, which is parallel to the horizon, at the same 
instant. During the next second the ball from the cannon 
reaches 5, while the other falls to 2, both having an equal de¬ 
scent. During the third second the projected ball will have 
spent nearly its whole force, and therefore its downward motion 
will be greater, while the motion forward will be less than before. 


What effect 223. Hence it appears that the horizontal 
^ffctile force mo ^ ton ^ oes n °t interfere with the action of 
on gravity? gravity , but that a projectile descends with 
the same rapidity while moving forward that it would 
if it were acted on by gravity alone. This is the neces¬ 
sary result of the action of two forces. 


What is the 224. The Random of a projectile is the horizontal 
Random of a .... , 

-projectile ? distance from the place whence it is thrown to the 

place where it strikes. 

At what angle 225. The greatest random takes place at an 
estVandom 01 ' an S ]e of 45 degrees; that is, when a gun is 
lake place / pointed at this angle with the horizon, the ball is 
thrown to the greatest distance. 


What will he 
the effect if a 
ball be thrown 
at arw angle 
above 45 de- 


Let Fig. 19 represent a gun or Fi S- 19 
a carronade, from which a ball 9° 
is thrown at an angle of 45 de- 


/ 


grees with the horizon. If 
^ 7 €es ' the ball be thrown at any angle 

above 45 decrees, the random will be the same 

O 7 

as it would be at the same number of degrees below 45 degrees.* 


•\ 

\ 


* A knowledge of this fact, and calculations predicated on it, enables the 
engineer so to direct his guns as io reach the object of attack when within 
the range of shot. 


6* 




NATURAL PHILOSOPHY. 


66 


What is tht 226. Centre oe Gravity. — It Las already 

Centre oj b ecn s t a ted [see Nos. 109 & 110] that the 
Gravity of a \ 

body ? Centre of Gravity of a body is the 'point 

around whi ~h all the parts balance each other. It is in 
other words, the centre of the weight of a body. 

^Cmtreof the ^27. The Centre of Magnitude is the central 
Magnitude ? point of the bulk of a body. 

Where is the 228. When a body is of uniform density, the 

cevtre of centre of gravity is in the same point with the 

gravity of a ° . 47 r 

body ? centre of magnitude. But when one part of the 

body is composed of heavier materials than another part, the 

centre of gravity (being the centre of the weight of the body) 

no longer corresponds with the centre of magnitude. 

Thus the centre of gravity of a cylinder plugged with lead is no. 
in the same point as the centre of magnitude. 

If a body be composed of different materials, not united in chemical 
combination, the centre of gravity will not correspond with the centre 
of magnitude, unless all the materials have the same specific gravity. 

When will a 229. When the centre of gravity of a body is 

^and when will su PP orted > the bod J itself will be supposed ; 
it fall ; but when the centre of gravity is unsupported, 
the body will fall.* 

vtfofDirec- ^30. ^ ^ ne drawn from the centre of grav- 
tion ? ity, perpendicularly to the horizon, is called 

the Line of Direction. 


231.. The line of direction is merely a line indicating the path 
which the centre of gravity would describe, if the body were per¬ 
mitted to fall freely. 


* The Boston School Apparatus contains a set of eight Illustrations for 
the purpose of giving a clear idea of the centre of gravity, and snowing the 
diiferonce between the centre of gravity and the centre of magnitude- 


MECHANICS. 


07 


When will a 232. When the line of direction falls within 

^and where will tlle baSe * ° f an y bod y> tbe bod y vdU stand J but 

it fall * when that line falls outside of the base, the 

body will fall, or be overset. 

Explain 233. (1.) Fig. 21 represents a loaded 
wagon on the declivity of a hill. The 
line C F represents a horizontal line, D E the base 
of the wagon. If the wagon be loaded in such a 
manner that the centre of gravity be at B, the per¬ 
pendicular B D will fall within the base, and the wagon will 
stand. But if the load be altered so that the centre of gravity 
be raised to A, the perpendicular A C will fall outside of the 
base, and the wagon will be overset. From this it follows that 
a wagon, or any carriage, will be most firmly supported when 
the line of direction of the centre of gravity falls exactly between 
the wheels; and that is the case on a level road. The centre of 
gravity in the human body is between the hips, and the base is 
the feet. 

234. So long as we stand uprightly, the line of direction falls 
within this base. When vve lean on one side, the centre of gravity 
not being supported, we no longer stand firmly. 

How does a 235. A rope-dancer performs all his feats of agil 
perjbrm^his by dexterously supporting the centre of gravity 
feats of agil- For this purpose, he carries a heavy pole in his 
tiy ? hands, which he shifts from side to side as he alters 

hh position, in order to throw the weight to the side which is 
deficient; and thus, in changing the situation of the centre of 
gravity he keeps the line of direction within the base, and he 
will not fall.t 


Fig. 21. 



C F 


Fig. 20. 


L 


1 

.Ell. 


* The base of a body is its lowest side. The base 
of a body standing on wheels or legs is represented by 
lines drawn from the lowest part of one wheel or leg 
to the lowest part of the other wheel or leg. 

Thus, in Figs. 20 and 21. D E represents the base of 
ihe wagon and ( of the table. .- 131r _ 

f The shepherds in the south of France afford an interesting instance of 
the application of the art of balancing to the common business of life. 
These men walk on stilts from three to four feet high, and their children* 











68 


NATURAL PHILO,':: PI Y. 


236. A spherical body will roll down a slope, because the centre 
of gravity is not supported.* 

237 Bodies, consisting of but one kind of substance, as wood, 
stone or lead, and whose densities are consequently uniform, will 
stand more firmly than bodies composed of a variety of substances, 
of different densities, because the centre of gravity in such cases 
more nearly corresponds with the centre of magnitude. 

238. When a body is composed of different materials, it will 
stand most firmly when the parts whose specific gravity is the 
greatest are placed nearest to the base. 

When will a 239. The broader the base and the nearer 
body stand 

most firmly ? the centre of gravity to the ground, the more 
firmly a body will stand. 

240. For this reason, high carriages are more dangerous than 
!nw ones. 

241 A pyramid also, for the same reason, is the firmest cf all 


Fig. 22. 



structures, because it has a broad base, and but little elevation. 


when quite young, are taught to practise the same art. By means of t.hes*. 
odd additions to the length of the leg, their feet are kept out of the water, 
or the heated sand, and they are also enabled to see their sheep at a greate* 
distance. They use these stilts with great skill and care, and run, jump 
and even dance on them, with great ease. 

* A cylinder can be made to roll up a slope, by plugging one side of it 
with lead ; the body being no longer of a uniform density, the centre of 
gravity is removed from the middle of the body to some point it, the lead 
as that substance is much heavier than wood. Now, in order that the cyl 
inder may roll d iwn the plane, as it is here situated, the centre of gravit) 
must rise, which is impossible ; the centre of gravity must always descend 
in moving, and will descend by the nearest and readiest means, which wib 
be by forcing the cylinder up the slope, until the centre of gravity is sup 
ported, and then it stops. 

A body also in the shape of two cones united at their bases can be mads 
to roll up an iuelined plane formed by two bars with their lower ends 
inclined towards each other. This is illustrated by a simple contrivance iri 
the “ Boston School Set, ” and the fact illustrated is called ie the mechanical 
oaradttJB '* 




















MECHANICS. 


bS) 


2-12. A cone has also the same stability ; hut, mathematically 
considered, a cone is a pyramid with an infinite number of sides. 
243. Bodies that have a narrow base are easily overset, because, 
they are but slightly inclined, the line of direction will fail out 


if 

side of the base, and consequently their centre of gravity will not be 
supported. 

Why can a 
person carry 
two pails of 
water more 
easily than 
one ? 


244. A person can carry two pails of water more 
easily than one, because the pails balance each 
other, and the centre of gravity remains supported 
by the feet. But a .single pail throws the centre 
of gravity on one side, and renders it more difficult to support 
the body. 

Where is the 245. Common Centre of Gravity of two 
^ty^of^two ^' Bodies. — When two bodies are connected, they 
bodies connect - are to be considered as forming but one body, and 
ed together l have hut one cen tre of gravity. If the two bodies 
be of equal weight, the centre of gravity will be in the middle 
of the line which unites them. But, if one be heavier than the 
other, the centre of gravity will be as much nearer to the heavier 
one as the heavier exceeds the light one in weight. 

Figures 23, 246 ‘ F «- 23 represents a T 

24, and 25. bar with an equal weight fast- “ 

ened at each end; the centre of gravity is 

at A, the middle of the bar, and whatever supports this centre 

will support both the bodies and the pole. 

247. Fig. 24 represents a bar with an Flg ‘ 24, 
unequal weight at each end. The centre of 
gravity is at C, nearer to the larger body. 



248. Fig. 25 represents a bar with un¬ 
equal weights at each ~nd, but the larger 
weight exceeds the less in such a degree 
that the centre of gravity is within the 
larger body at C.* 


Fig. 25. 



* There are no laws connected with the subject of Natural Sclonce so 
grand and stupendous as the laws of attraction. Long before the sublime 
tiat, “ Ltl there he lig/u t ” was uttered, the Creator’s voice was heard amid 







70 


NATURAL PHILOSOPHY. 


W/iat things 249. The Mechanical Powers. There 

in Mechanics . , 

require dis - are five things in mechanics which require a 

vnct consia- 4 ^}^ consideration, namely : 
eraiion 1 “ 

First , the power that acts. 

Secondly , the resistance which is to be overcome by the 
power. 

Thirdly , the centre of motion, or, as it is sometimes 
called, the fulcrum.* 

Fourthly , the respective velocities of the power and the 
resistance; and, 

the expanse of universal emptiness, calling matter into existence, and sub 
jecting it to these laws. Obedient to the voice of its Creator, matter sprang 
from “ primeval nothingness, ” and, in atomic embryos, prepared to cluster 
into social unions. Spread abroad in the unbounded fields of space, each 
particle felt that it was “ not good to be alone. ” Invested with the social 
power, it sought companionship. The attractive power, thus doubled by the 
union, compelled the surrounding particles to join in close embrace, and 
thus were worlds created. Launched into regions of unbound space, the 
new-created worlds found that their union was but a part of a great social 
system of law and order. Their bounds were set. A central point controls 
the Universe, and in harmonious revolution around this central point for 
ages have they rolled. Nor can one lawless particle escape. The sleepless 
eye of Nature’s law, vicegerent of its God, securely binds them all 

“ Could but one small, rebellious atom stray, 

Nature itself would hasten to decay.” 

With this sublime view of Creation, how can we escape the conclusion 
that the very existence of a law necessarily implies a Law-giver, and that 
Law-giver must be the Creator I Shall we not then say, with the Psalmist, 
“ It is the fool who hath said in his heart that there is no God ” 1 

Who, then, will not see and admire the beautiful language of Mr. Alison, 
while his heart burns with the rapture and gratitude which the sentiments 
are so well fitted to kindle : 

“ When, in the youth of Moses, * the Lord appeared to him in Iloreb,’ a 
/nice was heard, saying, ‘ Draw nigh hither, and put olf thy shoes from off 
thy feet, for the place where thou standest is holy ground.’ It is with such 
a reverential awe that every great or elevated mind will approach to the 
study of nature, and with such feelings of adoration and gratitude that he 
will receive the illumination that gradually opens upon his soul.” 

“ It is not the lifeless mass of ma ter, he will then feel, that he is exam¬ 
ining; it is the mighty machine of Eternal Wisdom, — the workmanship of 
Him ‘ in whom everything lives, and moves, and has its being.’ Under 
an aspect of this kind, it is impossil le to pursue knowledge without mingling 
with it the most elevated sentimen.s of devotion ; — it is impossible to per¬ 
ceive the laws of nature without [ erceiving, at the same time, the present 
and the providence of the Law-giver : — and thus it is that, in every age, 
the evidences of religion have advanced with the progress of true philosophy; 
and that science, in erecting a monument to her? elf, has, at the sau’s, 

ERECTED AN ALTAR TO THE DEITY.” 

* The word j'vXc, u m means a prop, or support 


THE MECHANICAL POWEiiS. 


71 


Fifthly , tlje instruments employed in the construction of 
the machine. 


250. (1.) The power that acts is the muscular strength of men 
or animals, the weight and momentum of solid bodies, the elastic 
force of steam, springs, the pressure of the air, the weight of 
water and its force when in motion, &c. 

(2.) The resistance to be overcome is the attraction of gravity 
or of cohesion, the inertness of matter, friction, &q 

(3.) The centre v of motion, or the fulcrum, is the point about 
which all the parts of the body move. 

(4.) The velocity is the rapidity with which an effect is pro¬ 
duced. 

(5.) The instruments are the mechanical powers which enter 
into the construction of the machine. 


t 251. The powers which enter into the construc- 
the Me- struction of a machine are called the Mechanical 
chamcal Powers. They are contrivances designed to in¬ 
crease or to diminish force, or to alter its direction. 


What is 252. All the Mechanical Powers are constructed 
darnen/ai on ^ ie principle that what is gained in power is 
principle lost in time. This is the fundamental law of 
fhankTl Mechanics. 

253. If 1 lb. is required to overcome the resistance of 2 lbs N 
the 1 lb. must move over two feet in the same time that the 
resistance takes to move over one. Hence the resistance will move 
only half as fast as the power ; or, in other words, the resistance 
requires double the time required by the power to move over a given 
space. 


Explain 254. Fig. 26 illustrates the principle as applied to the 
fig. 26. j ever> \y represents the weight, Fig. 26 . 

F the fulcrum, P the power, and the bar 
W F P the lever. To raise the weight W 
to w, the power P must descend to p. But, 
as the radius. of the circle in which the 
power P moves is double that of the radius 
of the circle in which the weight W moves. 




72 


NATURAL PHILOSOPHY. 


the arc P p is double the arc W w ; or, in other words, the dig 
tance P p is double the distance of W w. Now, as these dis* 
tances are traversed in the same time by the power and the 
weight respectively, it follows that the velocity of the power 
must be double the velocity of the weight; that is, the power 
must move at the rate of two feet in a second, in order to move 
weight one foot in the same time. 

This principle applies not only to the lever, but to all the 
Mechanical Powers, and to all machines constructed on me 
chanical principles. 

How many Me- 255. There are six Mechanical Powers: 
l m‘vlrC'and the Levor > the Wheel aud Axle > the Pull «y> 

their names ? the Inclined Plane, the Wedge and the Screw. 

All instruments and machines are constructed on the principle of one 
or more of the Mechanical Powers. 

All the Mechanical Powers may be reduced to three classes, namely • 
1st, a body revolving on an axis ; 2d, a flexible cord ; and, 3d, an inclined 
surface, smooth and hard. To the first belongs the lever, and the wheel 
and axle ; to the second, the pulley ; to the third, the inclined plane, the 
wedge and the screw. 

What is the 256. The Lever is an inflexible bar, mova- 
Lever , and how r , 

is it used ? ble on a lucrum or prop. 

It is used by making one part to rest on a fulcrum, applying the 
power to bear on another part, while a third part of the lever 
epposes its motion to the resistance which is to be overcome. 

257. In every lever, therefore, whatever be its form, there are 
three things to be distinctly considered, namely : the position of the 
fulcrum, of the power, and of the weight, respectively. It is the 
position of these which makes the distinction between the different 
kinds of levers. 

How many kinds 25 g There are three kinds f j 
of levers are ’ 

'here? called the first, second and third, according 

to the respective position of the fulcrum, the power, and 
the weight. 

These may be represented thus : 

Power, Fulcrum, Weight. 

Power, W eight, Fulcrum. 

Weight Power, Fulcrum 


THE MECHANICAL POWERS. 


73 


\\'IM is the 
position of the 
vower, the 
wet gut, and 
the fuicrum , 
respectively, in 
the tnree kinds 
of liver? 


That is, (1.) The power* is at one end, the 
weight at the other, and the fulcrum between them. 

(2.) Power at one end, the fulcrum at the 
other, and the weight between them. 

(3) The weight is at one end, the fulcrum at 
the other, and the power between them. 


Describe a -ever 
oj the first kind 
*>V figure 27, 
und tell the ad¬ 
vantage gained 


by it. 


Fig. 27 



259. In a lever of the first kind the fulcrum 
is placed between the power and the weight. 

Fig. 27 represents a lever of the first kind 
resting on the fulcrum 
F, and movable upon 
it. W is the weight to be moved, and B 
P is the power which moves it. The 
advantage gained in raising a weight , 
by the use of this hind of lever , is in 
proportion as the distance of the power from the fulcrum exceeds 
that of the weight from the fulcrum. Thus, in this figure, if 
the distance between P and F be double that between W and 
F, then a man, by the exertion of a force of 100 pounds with 
the lever, can move a wefght of 200 pounds. From this it fol¬ 
lows that the nearer the power is applied to the end of the lever , 
the greater is the advantage gained. Thus, a greater weight 
can be moved by the same power when applied at B than when 
it is exerted at P. 


On what prin¬ 
ciple is the com¬ 
mon steelyard 
constructed ? 

D'iscribe the 
steelyard. 


260. The common steelyard, an instrument for 
weighing articles, is constructed on the principle 
of the lever of the first kind. It consists oi a 
rod or bar, marked with notches to designate the 
pounds and ounces, and a weight, which is mova- 


* It is to be understood, in the consideration of all instruments and ma¬ 
chines, that some effect is to be producod by some power. The names 
f»/wer and weight are not always to be taken literally. They are terms 
used to express the cause and the effect. Thus, in the movement of a clock, 
the weight is the cause, the movement of the hands is the effect. The 
Cause of motion, whether it be a weight or a resistance, is technically called 
the power ; the effect, whether it be the raising of a weight, the overcoming 
of resistance or of cohesion, the separation of the parts of a body, oomnres 
*i*m ar expansion, is technically called the weight. 

7 


74 


NATURAL PHILOSOPHY. 


ole along the notches. The bar is furnished with three hooks, 
on the longest of which the article to be weighed is always to be 
hung. The other two hooks serve for the handle of the instru 



ment when in use. The pivot of each of these two hooks serves 
for the fulcrum. 

261. When suspended by the hook C, as in Fig. 

™} ai f $e 28, it is manifest that a pound weight at E will 
qtg tits ttiree * _ _, _ 

hooks in the balance as many pounds at W as the distance be- 

steelyardl tween the pivot of D and the pivot of C is con¬ 
tained in the space between the pivot of C and the ring from 
which E is suspended. 

The same instrument may be used to weigh heavy articles 
by using the middle hook for a handle, where, as will be seen 
in Fig. 29, the space between the pivot of F (which in this 
case is the fulcrum) and the pivot of D (from which the weight 
is suspended) being lessened, is contained a greater number of 
times in the distance betweeu the fulcrum and the notches on 
the bar. The steelyard is furnished with two sets of notches on 
opposite sides of the bar. An equilibrium * will always be 


Of Kqxiilibnurn. — In the calculations of the powers of all machines it i? 















THE MECHANICAL POWEltS. 


75 


pr<xlih,tc> when the product of the weights on the opposite sides 
ot the fulcrum into their respective distances from it are equal 
to one another. 



A balance, or pair of scales, is a lever of the first kind, with 
equal arms. Steelyards, scissors, pincers, snuffers, and a poker 
used for stirring the fire, arc all levers of the first kind. The 
longer the handles of scissors, pincers, &c., and the shorter tht. 
points, the more easily are they used. 

202. The lever is made in a great variety of forms and of many 
different materials, and is much used in almost every kind of 
mechanical operation. Sometimes it is detached from the fulcrum 

necessary to have clearly in mind the difference between action and equi¬ 
librium. 

By equilibrium is meant an equality of forces ; as, when one force is 
opposed by another force, if their respective momenta are equal, an equi¬ 
librium is produced, and the forces merely counterbalance each other. To 
proauce any action, there must be inequality in the condition of one of the 
forces. Thus, a power of one pound on the longer arm of a lever will bal 
ance a weight of two pounds on the shorter arm, if the distance of the 
power from the fulcrum be exactly double the distance of the weight from 
the fulcrum ; and the reason why they exactly balance is, because their 
momenta are equal. No motion can he produced or destroyed without a 
difference between the force and the resistance. In calculating the me¬ 
chanical advantage of any machine, therefore, the condition of equilibrium 
must first be duly considered. After an equilibrium is produced, whatever 
is added upon the one side or taken away on the other destroys the equi¬ 
librium, and causes the machine to move 














NATURAL PHILOSOPHY. 


!& 


t^ufc most generally the fulcrum is a pin or rivet by which the levet 
is permanently connected with the frame-work of other parts of the 
machinery. 

203. When two weights are equal, and the fulcrum is placed 
exactly in the centre of the lever between them, they will mutually 
balance each other; or, in other words, the centre of gravity being 
supported, neither of the weights will sink. This is the principle 
of the common scale for weighing. 


How is power 264. To gain power by the use of the 
usTof the t>ie l ever > the fulcrum must be placed near the 
lever? weight to be moved, and the power at the 

greater distance from it. The force of the lever , there¬ 
fore, depends on its length , together with the power 
applied , and the distance of the weight from the ful¬ 
crum.* 


Wha t is a 265. A Com - 

Cumpound pound Lever, rep- 

Ltver ? + i • w 

resented in Pig. 

30, consists of several levers, 

so arranged that the shorter 


Fig. 80. 



arm of one may act on the longer arm of the other. Great 
power is obtained in this way, but its exercise is limited to a 
very small space. 


Describe the 266. In a lever of the second kind, the fill- 

-/ itiv.d with. crum * s at one en( b the P ower at the other, and 
Fig. 31. the weight between them. 


(1.) Let Fig. 31 represent a lever of the second kind. F is 


the fulcrum, P the power, and W the weight. 
The advantage gained by a lever of this kind is 
in proportion as the distance of the power from 
the fulcrum exceeds that of the weight from the 
fulcrum. Thus, in this figure, if the distance 


Fig. 31. 



* This being the case, it is evident that the shape of the lever will not 
influence its power, whether it be straight or bent. The direct distance between 
the fulcrum and the weight, compared with the same distance between the 
fulcrum and the power, being the only measure of the mechanical advantage 
which it affords 
















THE MECHANICAL POWERS. 


Ti 


from P to F is four times the distance from W to F, then a 
power of one pound at P will balance a weight of four pounds 
at W. 

(2.) On the principle of this kind of lever, two persons, carrying 
a heavy burden suspended on a bar, may be made to bear unequal 
portions of it, by pi icing it nearer to the one than the other. 

267. fwo horses also, may be made to draw unequal port] jns of 
a load, by dividing the bar attached to the carriage in such a 
manner chat the weaker horse may draw upon the longer end of it. 

268. Oars, rudders of 
ships, doors turning on 
hinges, and cutting-knives 
which are fixed at one end, 
are constructed upon the 
principle of levers of the 
second kind.* 


Fig. 32. 



Describe the 269. In a lever of the third kind the fulcrum 

thirdkindby * S at 0ne en( *’ we S^ lt at ot ^ er > and the 
Fig. 38. power is applied between them. 

In levers of this kind the power must always exceed the 
weight in the same proportion as the distance of the weight 
1 rom the fulcrum exceeds that of the power from the fulcrum 
In Fig. 33 F is the fulcrum, W the weight, 


and P the power between the fulcrum and the f 
weight; and the power must exceed the weight 
in the same proportion that the distance between 
W and F exceeds the distance between P 
and F. 


Fig. 33. 


£i 


w 


270. A ladder, which is to be raised by the strength of a man’s 
arms, represents a lever of this kind, where the fulcrum is that 
end which is fixed against the wall; the weight may be consid¬ 
ered as at the top part of the ladder, and the power is the strength 
applied in raising it. 

271. The bones of a man’s arm, and most of the movable bones 
of animals, are levers of the third kind. But the loss of power in 
limbs of animals is compensated by the beauty and compactness of 


* It is on the same principle that, in raising a window, the hand should 
be applied to the middle of the sash, as it will then be easily raised; 
whereas, if the hand be applied nearer to one side than the other, the 
centre of gravity being unsupported, will cause the further side to bear 
against the frame, and obstruct its free motion. 











78 


NATURAL PHILOSOPHY. 


the limbs, as well as the increased velocity of their motion.. Tne 
wheels in clock and watch work, and in various kirds of machinery, 
mav be considered as levers of this kind, when the .power that 
moves them acts on the pinioq, near the centre of motion, and the 
resistance to be overcome acts on the teeth at the circumference. 
But here the advantage gained is the change of slow into rapid 
motion 

272. Practical Examples op Leverage. 


Questions for Solution 

(1.) Suppose a lever, 6 feet in length, to be applied to raise a weight of 50 pounds, 
with a power of only 1 pound, where must the fulcrum be placed? Ans. 1.41 in. + 

• (2.) Ifa man wishes to move a stone weighing a ton with a crow-bar 
6 feet in length, he himself being able, with his natural strength, to move a 
weight of 100 pounds only, what must be the greatest distance of the ful¬ 
crum from the stone 7 Ans. 8.42 in. + 

(II.) If the distance of the power from the fulcrum be eighteen time-i 
greater than the distance of the weight from .he fulcrum, what power would 
be required to lift a weight of 1000 pounds 1 Ans. 55.55 lb. -f- 

(4.) If the distance of the weight from the fulcrum be only a tenth of 
the distance of the power from the fulcrum, what weight can be raised by a 
power of 170 pounds 1 Ans. 1700 lb. 

(5.) In a pair of steelyards the distance between the hook on which the 
weight is hung and the hook by which the instrument is suspended is 2 
inches ; the length of the steelyards is 30 inches. How great a weight may 
be suspended on the hook to balance a weight of 2 pounds at the extremity 
cf the longer arm 1 Ans. 28 lb. 

(0.) Archimedes boasted that, if be could have a place to stand upon, he 
could move the whole earth. Now, suppose that he had a fulcrum with a 
lever, and that his weight, compared with that of the earth, was as 1 to 
270 millions. Suppose, also, that the fulcrum were a thousand miles from 
the earth; what must be his distance from the fulcrum ? 

Ans. 270,000,000,000 mi. 

(7.) Which will cut the more easily, a pair of scissors 9 inches long, 
with the rivet 5 inches from the points, or a pair of scissors 6 inches long, 
with the rivet 4 inches from the points 7 Ans. The first. 

(8.) Two persons, of unequal strength, carry a weight of 200 pounds 
suspended from a pole 10 feet long. One of them can carry only 75 pounds, 
the other must carry the rest of the weight. How far from the end of the 
pole must the weight be suspended 1 Ans. 8.75 ft. 

(9.) How must the whifiie-tree * of a carriage be attached, that one horse 
tnay draw but 3 cwt. of the load, while the other draws 5 cwt. 1 Ans. At J. 

(10.) On the end of a steelyard, 3 feet long, hangs a weight of 4 pounds. 
Suppose the hook, to which articles to be weighed are attached, to be at 
the extremity of the other end, at the distance of 4 inches from the hook 
by which the steelyards are held up. How great a weight can be estimated 
by the steelyjird 7 Ans. 32 lb. 

J&hmis uie~~ . 273. The Wheel and Axle. — The 
AUc! aUd Wheel and Axle consists of a cylinder with a 
wheel attached, both revolving around the same axis of motion. 


* The whiffle-tree is gererally attached to a carriage by a hook or 
leather band in the centre, sc that the draft shall bo equal on both eidoe 
Ibe hook or leather band thus becomes a fulcrum. 


THIi MECHANICAL POWERS. 


7l> 


Explain the 
construction of 
the wheel and 
axle by Fig. 
34. 


Fig. 34. 


How are the 274. The weight is supported by a rope or 
wdglfapplied chain wound around the cylinder; the power is 
to the wheel applied to another rope or chain wound around 
and axle ? the circumference of the cylinder. Sometimes 
projecting spokes from the wheel supply the place of the chain.* 

275. The place of the cylinder is sometimes supplied by a small 
wheel. 

276. The wheel and axle, though made in 
many forms, will easily be understood by in¬ 
specting Figs. 

34 and 35. In 
Fig. 34 P represents the larger 
wheel, where the power is ap¬ 
plied ; C the smaller wheel, or 
cylinder, which is the axle; 
and W the weight to be raised. 

What is the The advantage 

advantage gained is in 
gained by the 

use of the wheel proportion as 
and axle l the circumfer¬ 
ence of the wheel is greater 
than that of the axle. That 
is, if the circumference of the wheel be six times the circum¬ 
ference of the axle, then a power of one pound applied at the 
wheel will balance a power of six pounds on the axle. 

How do* the 277. Some- 
wheel and axle times the axle 



described in 

Fig. 35 differ 
from that de¬ 
scribed in Fig. 
34/ 

sometimes the 


is constructed 
with a winch or 
handle, as in 
Fig. 35, and 
wheel has pro¬ 
jecting spokes, as in Fig. 34. 



* A cylinder is a long circular body of uniform d mentor, with extremities 
forming equal and parallel circles. 





NATURAL PHILOSOPHY. 


8U 


_ . 278. The principle upon which the cel and 

On what prm- 1 ; . , . , „ , 

'iple is the axle 1S constructed is the same with tW.it ot the 

jheel and axle other Mechanical Powers, the want of powei 
const, acted l jj^g compensated by velocity. It is evident 
(from the Figs. 34 and 35) that the velocity of the circum¬ 
ference of the wheel is as much greater than that of the axle a:i 
it is further from the centre of motion; for the wheel describes 
a great circle in the same time that the axle describes a small 
one; therefore the power is increased in the same proportion as 
the circumference of the wheel is greater than that of the axle. 
If the velocity of the wheel be twelve times greater than that 
of the axle, a power of one pound on the wheel will support a 
weight of twelve pounds on the axle. 

279. The wheel and axle are sometimes called “ the perpetual 
lever ” the diameter of the wheel representing the longer arm, the 
diameter of the axle representing the shorter arm, the fulcrum 
being at the common centre. 

280. The capstan,* on board of ships and other vessels, is con 
structed on the principle of the wheel and axle. It consists of an 
axle placed uprightly, with a head or drum, pierced with holes for 
the lever, or levers, which supply the place of the wheel. 

281. Windmills, lathes, the common windlass, used for drawing 
water from wells, and the large wheels in mills, are all constructed 
on the principle of the wheel and axle. 

282. Wheels are a very essential part to most machines. They 
are applied in different ways, but, when affixed to the axle, their 
mechanical power is always in the same proportion ; that is, as 
the circumference of the wheel exceeds that of the axle, so much 
will the power be increased. Therefore, the larger the wheel, and 
the smaller the axle, the greater will be the power obtained. 


What are 
Cranks , and 
how are they 
made ? 


283. Cranks. — Cranks are sometimes con¬ 
nected with the axle of a wheel, either to give or 
to receive its motion. They are 
made by bending the axle in such a ^f. 6 * 

manner as to form four right angles facing in dif--I '- 

ferent directions, as is represented in Fig. 36. 

They are , in fact , nothing more than a double winch. 


* The difference between a capstan and a windlass lies only in the 
position of the wheel. If the wheel turn horizontally, it is called a capstan; 
it vertically, a windlass. 



THE MECHANICAL POWERS. 


81 


# 284. A rod connects the crank with other parts of the machinery 
either to communicate motion to or from a wheel. When the rod 
which communicates the motion stands perpendicular to the crank, 
which is the case twice during each revolution, it is at what is 
commonly called the dead point , and the crank loses all its power. 
But, when the rod stands obliquely to the crank, the cra_ik is then 
effective, and turns or is turned by the wheel. 

285. Cranks are used in the common foot-lathe to turn the wheel. 
Ihey are also common in other machinery, and are very convenient 
for changing rectilinear to circular motion, or circular to rectilinear 
280. \\ hen they communicate motion to the wheel they operate 
like the shorter arm of a lever; and, on the contrary, when they 
communicate the motion from the wheel they act like the longer 
arm. 


What are Fly- Fly-wheels are heavy rims of metal 

wheels , and secured by light spokes to an axle. They are 
what is their used to accumulate power, and distribute it 
equally among all the parts of a machine. They 
are caused to revolve by a force applied to the axle, and, when 
once set in motion, continue by their inertia to move for a long 
time. As their motion is steady, and without sudden jerks, 
they serve to steady the power, and cause a machine to work 
with regularity. 


288. Fly-wheels are particularly useful in connexion with cranks, 
especially when at the dead points , as the momentum of the fly¬ 
wheel, received from the cranks when they acted with most advan¬ 
tage, immediately carries the crank out of the neighborhood of the 
lead points, and enables it to again act with advantage. 

289. There are two ways in which the wheel and axle is sup¬ 
ported namely, first on pointed pivots, projecting into the extrem¬ 
ities of the axle,* and, secondly, with the extremities of the axle 
resting on gudgeons. As by the former mode a less extensive area 
is subjected to friction, it is in many cases to be preferred. 

How many ^90. Water-wheels.— There are three 
kinds oj kinds of Water-wheels, called, respectively, 


* The terms axle, axis, arbor and shaft, are synonymously used by 
mechanics to express the bar or rod which passes through the centre of a 
wheel. The terminations of a horizontal arbor are called gudgeons, and 
of an upright one frequently pivots ; but gudgeons more frequently denote 
the belts on which the extremities of the axle revolve, and pivots are 
either the pointed extremities of an axle, or short pins in the frame of a 
machine which receive the extremities of the axle. The term axis, in a 
more exact sense, may mean merely the.longest central diameter, or a 
diameter about which motion takes place 


NATURAL PHILOSOPHY. 


92 


Water-wheels the Overshot, the Undershot and th<* Breast 
are there? Wheel 

291. The Overshot Wheel receives its motion from the weight 

of the water flowing in at the top. 

Describe the Fig- 37 represents the Overshot Wheel. It con- 
Overshot sists of a wheel turning on an axis (not repre- 
Whed. sented in the figure), with Fig. 37. 

compartments called buckets, abed, &c., 
at the circumference, which are succes¬ 
sively filled with water from the stream 
S. The weight of the water in the buckets 
causes the wheel to turn, and the buckets, 
being gradually inverted, are emptied as 
they descend. It will be seen, from an 
inspection of the figure, that the buckets in the descending side 
of the wheel are always filled, or partly filled, while those in 
the opposite or ascending part are always empty until they are 
again presented to the stream. This kind of wheel is the most 
powerful of all the water-wheels. 

292. The Undershot Wheel is a wheel which is moved by the 
motion of the water. It receives its impulse at the bottom. 

Fig. 38 rep¬ 
resents the Un¬ 
dershot Wheel. 



Describe the 

Utulershot 

Wheel. 


Instead of buckets at the cir¬ 
cumference, it is furnished 
with plane surfaces, called 
float-boards, abed , &c., which 
receive the impulse of the 
water, and cause the wheel 
to revolve. —,— 



D. scribe the 293. The Breast Wheel is a wheel which receives 
Brca,t Wheel the water at about half its own height, or at the 







THE MECHANICAL POWEES. 


bA 


<evei of its own axis. It Pi g 39. 

is moved both by the 
weight and the motion 
cf the water. 

Fig. 39 represents a 
Breast Wheel. It is fur¬ 
nished either with buck¬ 
ets, or with float-boards, 
fitting the water-course, receiving the weight of the water with 
its force, while in motion it turns with the stream. 

294. In the -water-wheels which have now been described, the 
motion is given tu the circumference of the larger wheel, either by 
the weight of the water or by its force when in motion. 

295. All wheels used in machinery are connected with the differ¬ 
ent parts of the machine by other parts, called gearing. Sometimes 
they are turned by the friction of endless bands or cords, and some¬ 
times by cogs, teeth, or pinions. When turned by bands, the 
motion may be direct or reversed by attaching the band with one or 
two centres of motion respectively. 

296. When the wheel is intended to revolve in Fi s- 40 
the same direction with the one from which it 
receives its motion, the band is attached as in 
Fig. 40 ; but when it is to revolve in a contrary 
direction, it is crossed as in Fig. 41. In Fig. 40 Fig. 41. 
the band has but one centre of motion; in Fig. 41 
it has two. 

297. Instead of the friction of bands, the rough 
surfaces of the wheels themselves are made to com¬ 
municate their motion. The wheels and axles thus rubbing to 
gether are sometimes coated with rough leather, which, by increas¬ 
ing the friction, prevents their slipping over one another without 
communicating motion. 

298. Figure 42 represents soon a combination of wheels As 
the wheel a is turned by the weight S, its axle 
presses against the circumference of the wheel b, 
causing it to turn; and, as it turns, its axle rubs 
against the circumference of the wheel c, which 
in like manner communicates its motion to d. 

Now, as the circumference of the wheel a is equal 
to six times the circumference of its axle, it is 
evident that when the wheel a has made one rev¬ 
olution b will have performed only one-sixth of a 

4 revolution. The wheel a must therefore turn round six times to 
cause b to turn once. In like manner/) must perform six revolutions 
to cause c t^ turn once, and c must turn as many times to cause d to 


Fig. 42. 

d c b a 









NATURAL PHILOSOPIi/. 


34 


revolve once. Hence it follows that while d revolves once on 
axis c must revolve six times, b thirty-six times, and a two hundred 
and sixteen times. 

299. If, on the contrary, the power be applied at F, the conditions 
will all bo reversed, and c will revolve six times, b thirty-six, and a 
two hundred and sixteen timds. Thus it appears that we may 
obtain rapid or slow motion by the same combination of wheels. 


How may rapid or 
slow motion be ob¬ 
tained at pleasure 
by a combination of 
wheels with their 
axles'? 


300. To obtain rapid motion, the power 
must be applied to the axle; to obtain 
slow motion, the power must be applied to 
the circumference of the wheel. 


301. Wheels are sometimes moved by means of cogs or teeth 
articulating one with another, on the circumference of the wheel 
and the axle. The cogs on the surface of the wheels are generally 
called teeth, and those on the surface of the axle are called leaves. 
The axle itself, when furnished with leaves, is called a pinion. 

302. Fig. 43 represents a connexion of cogged wheels. The 
wheel B, being moved by a 
string around its circumfer¬ 
ence, is a simple wheel, with¬ 
out teeth. Its axle, being fur¬ 
nished with cogs or leaves , to 
which the teeth of the wheel 
D are fitted, communicates its 
motion to D, which, in like 
manner, moves the wheel C. 

The power P and the weight 
W must be attached to the 
circumference of the wheel or 
of the axle, according as a slow 
or a rapid motion is desired. 

303. Wheels with teeth or cogs are of three kinds, according tc 




the position of the teeth. When the teeth are raised perpendicular 
to the axis, they are called spur wheels or spur gear. When the 
t<*eth are narallel with the axis, they are '-ailed crown wheels. When 


Fig. 44. 


Fig. 45. . 








THE MECHANICAL POWERS 


85 


lhe J raised on a surface inclined to the axis, they are called 
levelled wheels. In Fig. 43 the wheels are spur wheels In Figs. 
44 and 45 the wheels are bevelled wheels. 

304. Different directions may be given to the motion produced 
by wheels,, by varying the position of their axles, and causing them 
to revolve in different planes, as in Fig. 44 ; or by altering the shape 
and position of the cogs, as in Fig. 45. 

H°w may the 305. The power of toothed wheels may be 
power of toothed . , , , ^ . , ,, 

wheels be esti - estimated »y substituting the number of teeth 

mated ? in the wheel and the number of leaves in the 

pinion for the diameter or the circumference of the wheel and 

axle respectively. 

306. Suspension of Action. — In the arrangement of machinery, 
it is often necessary to cut off* the action of the moving power from 
some parts, while the rest continues in motion. This is done by 
causing a toothed wheel to slide aside in the direction of its axis to and 
from the cogs or leaves into which it articulates, or, when the motion 
is communicated by a band, by causing the band to slip aside from 
the wheel to another wheel, which revolves freely around the axle, 
without communicating its motion. 

307. Wheels are used on vehicles to diminish the friction of the 
road. The larger the circumference of the wheel, the more readily 
it will overcome obstacles, such as stones or inequalities in the 
surface of the road. 

308. A large wheel is also attended with two additional advan¬ 
tages , namely, first, in passing over holes, ruts and excavations, a 
large wheel sinks less than a small one, and consequently causes less 
jolting and expenditure of power; and, secondly, the wear of large 
wheels is less than that of small ones, for, if wesuppose awheel six 
feet in diameter, it w r ill turn round but once while awheel three feet 
in diameter will turn round twice, its tire will come twice as often 
to the ground, and its spokes will twice as often have to bear the 
weight of the load. 

309. But w r heels must be limited in size by two considerations : 
first, the strength of the materials ; and secondly, the centre of the 
wheel should never be higher than the breast of the horse, or other 
animal by which the vehicle is drawn ; for otherwise the animal 
would have to draw obliquely downward, as well as forward, and 
thus expend part of his strength in drawing against the ground.* 

* In descending a steep hill, the wheels of a carriage are often locked (ai 
it is called), that is, fastened in such a manner as to prevent th.eir turning , 
and thus thn rolling is converted into the sliding friction, and the vekicl< 
descends more safely. 

Castors are put on the legs of tables and other articles of furniture, ts 
facilitate the moving of them ; and thus the sliding is iouverted into tiw 
rolling friction. 


8 


86 . 


NATURAL PHILOSOPHY. 


310. Practical Examples of Power applied to the Tv heel and Axls. 

Questions for Solution. 

(1.) With a wheel 5 feet in diameter and a power of 6 pounds, whai 
aaust be the diameter of the axle to support 3 cwt. 1 Ans. 1.2 in. 

(2.) How large must be the diameter of the wheel to support with 10 
lbs. a weight of 5 cwt. on an axle 0 inches in diameter 1 Ans. 87.5ft. 

(3.) A wheel has a diameter of 4 ? eet, an axle of 6 inches. What power 
must be applied to the wheel to balance 2 cwt. on the axle l . Ans. 25 lb. 

(4.) There is a connexion of cogged wheels having G leaves on the pinion 
and 3G cogs on the wheel. What is the proportion of the power to the 
weight in equilibrium 1 Ans. As 1 to 6. 

(5.) Suppose a lever of six feet inserted in a capstan 2 feet in diameter, 
and six men whose united strength is represented by i of a ton at the capstan, 
bow heavy an anchor can they draw up, allowing the loss of £ of their power 
from friction 1 Ans. 2 T. 

(G.) What must be the proportion of the axle to the wheel, to sustain a 
weight 30 cwt. with a power of 3 cwt. 'I Ans. As 1 to 10. 

(7.) The weight is to the power in the proportion of six to one. What 
must be the proportion of the wheel to the axle 1 Ans. 6 to 1. 

(S.) The power is represented by 10, the axle by 2. How can you repre- 
eer t the wheel and axle 1 Ans. 10: weight:-. 2: wheel. 

(9.) The weight is expressed by 15, the power by 3. What will repre¬ 
sent the wheel and axle 1 Ans. 5 and 1. 

(10.) The axle is represented by 16, the power by 4. Required the pro 
portion of the wheel and axle. Ans. 4:weight::16:wfuel. 

(11.) What is the weight of an anchor requiring 6 men to weigh it, by 
means of a capstan 2 feet in diameter, with a lever 8 feet long, 2 feet of its 
length being inserted in the capstan ; supposing the power of each mail to 
be represented by 2 cwt., and a loss of 1 the power by friction? Ans. 56 cwt. 

(12.) A stone weighing 2 tons is to be raised by a windlass with spokes 
2 feet in length, projecting from an axle 9 inches in diameter. IIow many 
men must be employed, supposing each man’s power equal to 2 cwt., and the re¬ 
sistance increased £ by friction ? Amt. 5 men. 

What is a 311. The Pulley. —The Pulley is a small 
Valley * wheel turning on an axis, with a string or rope 
in a groove running around it. 

How many kinds There are two kinds of pulleys — the 

oj pulleys are 1 J 

there * fixed and the movable. The fixed pulley 

is a pulley that has no other motion than a revolution on 

its axis, and it is used only for changing the direction of 

motion. 

Explain 312. Fig. 46 represents a fixed pulley. P is a 
Fig. 46. gma p w heel turning on its axis, with a string running 
round it in a groove. W is a weight to be raised, F is the force 
or power applied. It is evident that, by pulling the string at 
F, the weight must rise just as much a3 the string is drawn 


THE MECHANICAL POWERS. 


*7 


flown. As, therefore, the velocity of the weight and the Fig. ^ 
power is precisely the same, it is manifest that they 
balance each other, and that no mechanical advantage 
is gained.^ But this pulley is very useful for changing 
1 the direction of motion. If, for instance, we wish to * 
raise a weight to the top of a high building, it can be done 
with the assistance of a fixed pulley, by a man standing 
below. A curtain, or a sail, also, can be raised by means of a 
fixed pulley, without ascending with it, by drawing down a string 
running over the pulley. 


r i 


On what prin¬ 
ciple does the 
fixed pulley act ? 

of gravity, the 


313. The fixed pulley operates on the same 
principle as a lever of the first kind with equal 
arms, where the fulcrum being in the centre 
power and the weight are equally distant from it. 


and no mechanical advantage is gained. 

O O 


314. The movable pulley differs from 
the fixed pulley by being attached to Fig. 47 . 
the weight; it therefore rises and 
falls with the weight. 

315. Fig. 47 represents a movable pulley, 
with the weight W attached to it by a hook 
below. - One end of the rope is fastened at F; and, as 
the power P draws the weight upwards, the pulley 
rises with the weight. Now, in order to raise the 
weight one inch, it is evident that both sides of the string 


How does the 
movable pulley 
differ from the 
fixed 1 


Explain 
Fig. 47. 



* Although the fixed pulley gives no direct mechanical advantage, a 
man may advantageously use his own strength by the use of it. Thus, if 
ne seat himself on a chair suspended from one end of a rope passing over a 
fixed pulley, he may draw himself up by the other end of the rope by exert¬ 
ing a force equal only to one-half of his own weight. One half of his weight 
is supported by the chair and the other half by his hands, and the effect is 
tne same as if he drew only one half of himself at a time ; for, the rope being 
doubled across the pulley, two feet of the rope must passthrough hi3 hands 
before he can raise himself one foot. In this manner laborers and others 
frequently descend into wells, and from the upper floors of stores, by meant 
of a rope passing over a fixed wheel < r pulley. 




88 


NATURAL PHILOSOPHY. 


must be shortened; in order to do which, the power P must 
pass over two inches. As the velocity of the power is double 
that of the weight, it follows that a power of one pound will bal¬ 
ance a weight on the movable pulley of two pounds.* 


What is the ad- 310, The power gained by the use of pul- 
buhfnJTihe le J* is ascertained by multiplying the num- 
mo cable pulley? ber of movable pulleys by 2.f 


317. A weight of 72 pounds may be balanced by a power of 9 
pounds with four pulleys, by a power of 18 pounds with two pul¬ 
leys, or b}' a power of 3G pounds with one pulley. But in each 
case the space passed over by the power must be double the space 
passed over by the weight, multiplied by the number of movable 
pulleys. That is, to raise the weight one foot, with one pulley, the 
power must piles over two feet, with two pjulleys four feet, with 
four pulleys eight feet. 


Explain 318. Fig. 48 represents a system of fixed and 
Fig. 48. m0V able pulleys. In the block F there 
are four fixed pulleys, and in the block M there 
are four movable pulleys, all turning on their com¬ 
mon axis, and rising and falling with the weight 
W. The movable pulleys are connected with the 
fixed ones by a string attached to the hook H, 
passing over the alternate grooves of the pulleys 
in each block, forming eight cords, and terminating 
at the power P. Now, to raise the weight one foot, 
it is evident that each of the eight cords must be 



* Thus, it is seen that pulleys act on the same principle with the lever 
and the wheel and axle, the deficiency of the strength of the power being 
compensated by superior velocity. Now, as we cannot increase our natural 
stiength, but can increase the velocity of motion, it is evident that we are 
enabled, by pulleys, and other mechanical powers, to reduce the resistance 
or weight of any body to the level of our strength. 

t This ru i e applies only to the movable pulleys in the same block, or 
when the parts of the rope which sustains the weight are parallel to each 
other. The mechanical advantage, however, which the pulley seems to posses" 
in theory, is considerably diminished in practice by the stiffness of the ropes 
and the friction of the wheels and blocks. When the parts of the cord, 
also, are not parallel, the pulley becomes less efficacious ; and when the 
parts of the cord which supports the weight very widely depart from par¬ 
allelism, the pulley becomes wholly useless. There are certain arrange¬ 
ments of the mrd and the pulley by which the effective power of the 







THE MECHANICAL POWEHS. 


S'«5 


shortened one foot, and, consequently, that the power P must 
descend eight times that distance. The power, therefore, must 
pass over eight times the distance that the weight moves. 

319. The movable pulley, as well as the fixed, acts on the same 
principle with the lever, the deficiency of the strength of the 
power with the movable pulley being compensated by its superior 
velocity. 

On what princi- 320. The fixed pulley acts on the principle of 
pie is the mov- a lever with equal arms. [See No. 313.] The 
ftructcd? C ° n ~ movable Pulley, on the contrary, by giving a 
superior velocity to the power, operates like a 
lever with unequal arms. 

321. Practical use of Pulleys . — Pulleys are used to raise goods 
into warehouses, and in ships, &c., to draw up the sails. Both kinds 
of pulleys are in these cases advantageously applied : for the sails 
are raised up to the masts by the sailors on deck by means of the 
fixed pulleys, while the labor is facilitated by the mechanical power 
of the movable ones. 

322. Both fixed and movable pulleys are constructed in a great 
variety of forms, but the principle on which all kinds are con¬ 
structed is the same. What is generally called a tackle and fall , 
or a block and tackle, is nothing more than a pulley. Pulleys have 
likewise lately been attached to the harness of a horse, to enable 
the driver to govern the animal with less exertion of strength. 


^ ^ ^ 323. It may be observed, in relation to the Me- 

plies' to™ithe chanical Powers in general, that power is alivays 
Mechanical gained at the expense of time and velocity ; that 
is, the same power which will raise one pound in 
one minute will raise two pounds in two minutes , six pounds in 
six minutes , sixty pounds in sixty minutes, §-c.: and that the 
same quantity of force used to raise two pounds one foot will 
raise one pound two feet, $c. And, further, it may be stated 
that the product of the weight multiplied by the velocity of the 
weight will always be equal to the product of the power multi¬ 
plied by the velocity of the power. 


pulley may be augmented in a three-fold in«tead of a two-fold proporti >n 
3>ut, when such an advantage is secured, it must be by contriving to muk« 
the power pass over three times the space of the weight 
8 * 


NATURAL PHILOSOPHY. 


<J0 


In what pr opor¬ 
tion is the power 
to the weight 
when the mov¬ 
able pulley is 
used t 


Hence we have the following rule \ The 
power is in the same proportion to the 
weight as the velocity of the weight xs to 
the velocity of the power* 


324. Practical Examples of Application of the Pulley. 

Questions for Solution. 

(1.) Suppose a power of 9 lbs. applied to a set of 3 movable pulleys. Al 
lowing $ loss for friction, what weight can be sustained by them 1 A. 36 lb. 

(2.) Six movable pulleys are attached to a weight of 1800 lbs.; what 
power will support them, allowing a loss of two-thirds of the power from 
friction 1 Ans. 4.50 lb. 

(3.) Six men, with a block and tackle containing nine movable pulleys, 
are required to raise a sail. Suppose each man’s strength to be represented 
by two cwt. and two-thirds of the power lost by friction, what is the 
weight of the sail, with its appendages 1 Ans. 72 cwt 

(4.) If a stone weighing 3 tons is to be raised by horse power to the wall 
of a building in process of erection, by means of a derrick from which are 
suspended 3 movable pulleys, how many horses must be employed, sup¬ 
posing each horse capable of drawing as much as eight men, each of whom 
can lift 2 cwt., making an allowance of two-thirds for friction 1 Ans. If. 

(5.) A block contains 5 movable pulleys, connected with a beam contain¬ 
ing 5 fixed pulleys. A weight of half a ton is to be raised. Allowing a loss 
of two-thirds for friction, what power must be applied to raise it 1 A. 8 cwt 

(7.) The power is 3, the weight is 27; how many pulleys must be used, 
if friction requires an allowance of two-thirds I Ans. 27, 

(8.) Friction one-third of the power, power 6, weight 72, — how many pul¬ 
leys 1 Ans. 18. 

(9.) Weight 84, friction nothing, pulleys, 3 fixed, 3 movable ; required 
the power. Ans. 14 

(10.) Power 12, friction 8, four pulleys, two of them fixed ; required the 
weight. Ans. 16. 

(11.) Six movable and six fixed pulleys. The weight is raised 3 feet. 
How far has the power moved 1 Ans 36 ft. 

^12.) The power has moved 12 feet ; how far has the weight moved un¬ 
der two pulleys, one fixed, the other movable 1 Ans. 6ft. 

(13.) The weight, suspended from a fixed pulley, has moved 6 feet. How 
far has the power moved 1 Ans. 6 ft. 

(14.) The power has moved 29 feet under a fixed pulley ; how far has 
the weight moved 1 Ans. 20 ft. 

What is the In- 325. TlIE INCLINED PLANE.— The In- 
clmed Plane? clined Plane consists of a hard plain surface, 
inclined to the horizon. 

320. The principle on which the inclined plane acts as a me¬ 
chanical power is simply the fact that it supports part of the weight. 
[f a body be placed on a horizontal plane, its whole weight will be 


* The stiffness of the cords and the friction of the blocks frequently 
require large deduction to be made from the effective power of pulleys 
The loss thus occasioned will sometimes amount to two-thirds of the povror 


THE MECHANICAL POWERS. 


91 


supported , but, if the plane be elevated at one end, by degrees, it 
will support less of the weight in proportion to the elevation, untn 
the plane becomes at right angles to the horizon, when it will sup¬ 
port no part of the weight, and the body will fall perpendicularly. 

**27. A body, in ascending or descending an inclined plane, wil. 
have a greater space to traverse than if it should rise or fall per¬ 
pendicularly. The time, therefore, of its ascent or descent will be 
longer, and thus it will oppose less resistance, and thus, also, a less 
force will be required to cause its ascent. Hence, we see that the 
fundamental principle of Mechanics, “ What is gained in power is 
lost in lime,” applies to the Inclined Plane as well as to the Me¬ 
chanical Powers that have already been described. 

What is the ad- 328. The advantage gained by the use of 

vantage gained .7 J . 

by the use of the tiie inclined plane is in proportion as the 

inclined plane ? length of the plane exceeds its perpen¬ 
dicular height. 


Fig. 49 represents an inclined plane. C A 
its length, and W a weight which is to be 
moved on it. If the length C B be four 
times the height C A then a power of one 
pound at C will bal 'nee a weight of four b-^ 
pounds on the incline 1 plane C B. 


its height, C B 


Fig. 49. 



329. The greater '.he inclination of the plane, the greater must 
be its perpendicular height, compared with its length ; and, of 
course, the greater must be the power to elevate a weight along its 
surface. 

330. Instances of the application of the inclined plane are very 
common. Sloping planks or pieces of timber leading into a cellar, 
and on which casks are rolled up and down; a plank or board with 
one end elevated on a step, for the convenience of trundling wheel¬ 
barrows, or rolling barrels into a store, &c., are inclined planes. 

331. Chisels anl other cutting instruments, which are cham¬ 
fered, or sloped on* r on one side, are constructed on the principle 
of the inclined pla^e.* 

332. Roads wlr ih are not level may be considered as inclined 
planes, and the in lination of the road is estimated by the height 
corresponding to s ime proposed length. To raise a load up an 
inclined plane rev>uires a power sufficient to carry it along the 
whole distance of the length of the base, and then to lift it up to 


* Chisels for cutting wood should have their edges at an angle of about 
8C C ; for cutting ; ron from 50-' to 60°, and for cutting brass at about 80° or 
{T ' Tools urged by pressure may be sharper than those which, like the 
v >dge, are driven by percussion 



92 


NATURAL PHILOSOPHY. 


the elevation ; but in the inclined plane a feebler fore «vill accoiu 
plish the desired object, because the resistance is s', ead equally 
over the whole distance.* 

What is the .833- The Wedge.— TLe Wedge consists 
Wedge? 0 f t w0 inclined planes united at their bases. 

What is the ad- 334. The advantage gained by the wedge 
ly^hfusToftt 13 in proportion as its length exceeds the 
wtdge? thickness between the converging sides. 

In what pro¬ 
portion is the It follows that the power of the wedge is in pio- 
power of the portion to its sharpness. 
wedge ? 

, • Fi<* 60 

335. Fig. 50 represents a wedge. The line ah °' a ' 
represents the base of each of the inclined planes 
of which it is composed, and at which they are 
united. 

b 

336. The wedge is a very important mechanical power, used to 
split rocks > timber, &c., which could not be effected by any other 
power.f 

337. Axes, hatchets, knives, and all other cutting instruments, 
chamfered, or sloped on both sides, are constructed on the principle 
of the wedge; also pins, needles, nails, and all piercing instru¬ 
ments. 



On what does 
the effective 
power of the 
wedge depend ? 


338. The effective power of the wedge depends 
on friction ; for, if there were no friction, the 
wedge would .fly back after every stroke. 


* Mention has already been made of the sagacity of animals in a former 
page [.vee No. 54], and a sort of intuitive knowledge which they appear 
to possess of philosophical principles. In ascending a steep hill, a common 
dray-horse will drag his load from side to side, as if he were conscious that 
he thus made the plane longer in proportion to its height, and thereby 
made bis load the lighter. 

t The wedge is an instrument of exceedingly effective power, and is 
frequently used in presses for extracting the juice of seeds, fruits, &c. It 
is used especially in the oil mill , by which the oil is extracted from seeds. 
The seeds are placed in hair bags, between planes of hard wood, which are 
pressed together, by wedges. The pressure thus exerted is so intense that 
the seeds, after the extraction of the oil, are converted into masses as hard 
and compact as the most dense woods. 

Wedges are used also in the launching of vessels, and also for restoring 
Endings to the perpendicular which have been inclined by the sinking 0 / 
the foundation. 




THE MECHANICAL POWERS. 


y3 

3.^9. 'Hie wedge derives much of its power from the force of per 
eussion, which in its nature is so different from continued force, 
such as the pressure of weights, the force of springs, &c., that it 
would be difficult to submit it to numerical calculation ; and, there¬ 
fore, we cannot properly represent the proportion which a blow 
bears to the weight. 

What is the 340. The Screw. — The Screw is an in- 
&rew? clined plane wound around a cylinder, thus 
producing a circular inclined plane, forming what is called 
the threads of the screw. 

341. Cut a piece of paper in the shape of an inclined plane, as 
represented by Fig. 49, and, beginning with the end represented 
by the height - C A, in that Figure, wind it around a pencil, or a 
round ruler. The edge of the paper will be a circular inclined plane, 
and will represent the threads of the screw. The distance between 
any two threads on the same side of the rule will represent the per¬ 
pendicular height of the inclined plane that extends once around the 
cylinder, and the advantage gained in the use of the screw (when 
used without a lever) will be the same as in the inclined plane; 
namely, as the length of the plane exceeds the perpendicular height. 
But the screw is seldom used alone. A lever is generally attached 
to the screw, and it is with this attachment the screw will now be 
considered. 


t j e 342. The Screw is generally accompanied 
Generally attends by an appendage called the nut , which consists 
the Screw ? of a concave cylinder or block, with a hollow 

spiral cavity cut so as to correspond exactly with the threads of 
the screw. When thus fitted together, the screw and the nut 
form two inclined planes, the one resting on the other. 

343. Sometimes the screw is movable and 
Is the screw, or . 

the nut mov- the nut is stationary, and sometimes the screw 
able ? is stationary and the nut is movable. 

344. At every revolution the screw or the nut advances or 
retreats through a *pace equal to the distance between the threads 
of the screw. 


In what manner 
does the power 
upplied to the 
uttvw move ? 


345. The power applied to a screw generally 
describes a circle around the screw, perpendic¬ 
ular to the plane in which the screw or nui 


moves. 


94 


NATURAL PHILOSOPHY. 


metis the aJvan- 846 - The advantage gained by the 
tag-.: gamed by the screw is in proportion as the circumfer¬ 
ence described by the power exceeds the 
distance between the threads of the screw. 


What is meant by 347. The cylinder with its threads is called 

the Convex and the Convex Screw, and the nut is called the 
Concave Screw J a mi 

Concave Screw, lhe lever is sometimes at* 

tached to the screw, and sometimes to the nut. 



Explain 348. Fig. 51 represents a fixed screw Fi s- 61 * 
tig. 51. g^ with a movable nut N, to which is 
attached the lever L. By turning the lever in one 
direction the nut descends, and by turning it in the 
opposite direction the nut ascends, at every revo¬ 
lution of the lever, through a space equal to the dis¬ 
tance between the threads of the screw ; to accomplish which, the 
hand or power applied to the end of the lever L will describe a 
circle around the screw S, of which the radius is L S. The 
power thus passes over a space represented by the circumfer¬ 
ence of this circle, and the advantage gained i3 in the same pro¬ 
portion as the space exceeds the distance between each threa 
of the screw 


Explain 349. Fig. 52 represents a movable Fi s- 62 * 

Fig. 52. gcrew> with a nut fixed in a frame, and 
consequently immovable. As the lever L is 
turned, the screw ascends or descends at every 
revolution of the lever through a space equal to 
the distance between the threads of the screw, and 
the advantage gained is in the same proportion as in the case of 
the movable nut in Fig. 51. 

350. It will thus be seen that, although the screw is usually con-^ 
sidered distinctly as a mechanical power, it is in fact a compound 
power, consisting of two circular inclined planes, moved by a lever. 

351. The power of the screw being estimated by the distance 
between the threads, it follows that the closer the threads are 
together, the greater will be the power, but the slower will be tho 
tort ion produced; for. every revolution of the lever advances the 










THE MECHANICAL POWEKS. 


95 


Rerow oi the nut only through a space as great as the distance of the 
threads from each other. 

352 Ihe screw is applied to presses and engines of all kinds 
where great power is to be applied, without percussion, through 
small distances It is used in bookbinders’ presses, in cider and 

Fig. 53. 



wine presses, in raising buildings. It is also used for 
coining, and for punching square or circular holes 
through thick plates of metal. When used for this 
purpose, the lever passes through the head of the 
screw and terminates at both ends with heavy 
balls or weights, the momentum of which adds to 
the force of the screw, and invests it with immense 
power. 

353. Hunter’s Screw. — The ingenious contrivw»ee known by 
the name of Hunter’s Screw consists of two screw? of different 
threads playing one within the other ; and such will be the effect, that 
while one is advancing forward the other will retreat, and the resist¬ 
ance will be urged forward through a distance equal only to the 
difference between the threads of the two screws. An indefinite 
increase in the pow r er is thus obtained, without diminishing th* 
thread of the screw". * 

* From what has been stated with regard to the Mechanical Powers, it 
appears that by their aid a man is enabled to perform woiks to which hi. 
unassisted natural strength is wholly inadequate. But the power of ali 
machines is limited by the strength of the materials of which they are com¬ 
posed. Iron, which is the strongest of all substances, will not resist a strain 
beyond a certain limit. Its cohesive attraction may be destroyed, and it 
can withstand no resistance which is stronger than its cohesive attraction. 
Besides the strength ol the materials, it is necessary, also, to consider the 
time which is expended in the application of mechanical assistance. Archim¬ 
edes is said to have boasted to Iliero, King of Syracuse, that, if he would 
givo him a place to stand upon, he would move the whole world. In orde- 
to do this, Archimedes must himself have moved over as much more space 
than he moved the world as the weigh. of the world exceeded his own weight; 
e nd it has been computed that he must have moved with the velocity of a 
Cannon-ball for a million of years, in order to move the earth the twenty 
vtven millionth part of an inch. 


Fib 64. 













NATURAL PHILOSOPHY. 




$54. IhtACTicAL Examples of the Application of the Inclined Plane 

and the Screw. 

Questions for Solution. 

(1 ) With an inclined plane the power moves 16 feet, the power is to the 
Weight as 6 to 24. How far does the weight move 1 Ana. 4 e t. 

(2.) The length of an inclined plane is 5 feet, the proportion of the 
power to the weight is as 2 to 10. What is the height of the plane ? A. 1 ft. 

(3.) An inclined plane is 4 feet high, a power of 6 lbs. draws up 30 
tbs. What is the length of the plane ' Ana. 20ft. 

(4.) The length of a plane is 12 feet, the height is 3 feet. What is the 
proportion of the power to the weight to oe raised 1 Ana. As 1 to 4. 

(5 ) The distance between the threads cf a screw is 1 inch, the length of 
toe lever is 2 feet. What is the proportion Ana. 1 to 150.79 + 

(6.) Which will exert the greater force, a lever 3 feet long with the 
fulcrum 6 inches from one end, or a screw with a distance of 1 inch between 
the threads and a lever one foot long 1 Ana. The screw. 

(7.) A screw with the threads 2 inches apart, and a lever 6 feet long, 
draws a ship of 200 tons up an inclined plane whose length is to the height in 
the proportion of 1 to 16. What power must be applied to the lever of the 
rcrew ? Ana. 11.05 lb. + 

(8.) If a man can lift a weight of 150 lbs., how much can he draw up an 
inclined plane whose length is to its height as X4 to 3? Ana. 1200 lb. 

(0.) A Hunter’s screw has a lever four feet long. The distance between 
the threads of the larger screw is 1 inch, between those of the smaller S of an 
inch. How much weight can a man whose power is represented by 175 lbs. 
move with such a screw 1 Ana. 211115.52 lb. 

(10.) A screw with a lever of 2 feet in length, and a distance of 4 of an 
inch between its threads, acts on the teeth or cogs of a wheel whose diameter 
is to that of the axle as 4 to 1. Fastened to the axle is a. rope, one end of 
which is attached to a weight at the bottom of an inclined plane, the length 
of which is to the height as 12 to 3. Suppose this weight to require the 
strength of a man who can lift 200 lbs. to be applied to the lever of the 
screw to move it. What is the weight I Ana. 965099.5200 lb. 

What is the 355. TlIE KNEE JOINT, OR TOGGLE 
Toggle Joint’ JolNT _ The Toggle j 0int)0r Kn ee joint, 

consists of two bars united by a hinge or ball and socket, 
which, being urged by a power perpendicular to the resistance, 
acts with rapidly-increasing force, until the bars form a 
straight line. 

The toggle (or knee) joint affords a very useful mode of convert¬ 
ing velocity into power, the motion produced being very nearly at 
right angles with the direction of the force. It is a combination 
of levers, and the same law applies to it as to all machinery, 
namely, that the power is to the resistance inversely as the sp&e« 
of the power is to the space of the resistance. 



PHE MECHANICAL POWERS. 


97 


Explain 356. Fig 55 represents a toggle joint. 
^* 6 - 55. ^ C and B G are the two rods con¬ 

nected by a joint at G. A moving force applied 
at G, in the direction G D, acts with great and 
constantly increasing power to separate the parts 
A and B. 



357. The operation of the toggle 
|oint is seen in the iron joints which 
are used to uphold the tops of chaises. 
It is also used in various kinds of 
printing-presses to obtain the great¬ 
est power at the moment of impres¬ 
sion.* 

358. Media. — The motion of all 
bodies is affected by the substance or 
element in which they move, and by 
which they are on all sides surround¬ 
ed. Thus the bird flies in the air, the 
fish swims in the water. Air there¬ 
fore is the medium in which the for¬ 
mer moves, while water is the medium 
in which the motion of the latter is 
made. 


Fig. 56. 



What is a 
Medium I 


359. A Medium is the substance, solid or fluid, 
which surrounds a body, and which the body must 
displace as it moves. 


3G0. When the fish swims or the bird flies, each must force its 
way through the air or the water ; and the element thus displaced 
must rush into the spot vacated by the body in its progress. It has 
already been stated that the body of the fish or of the bird is pro- 
spelled in its motion in the one case bvthe reaction of the air on the 
wings of the bird, and in the other of the water on the fins of a fish. 
The fish moves in the denser medium and needs therefore to present 
a less surface for the reaction of the water ; while the bird, living in 
a comparatively rare medium, presents in his wings a much larger 
extent of surface to receive the reaction of the air. In making 
the fins of a fish, therefore, so much smaller, in proportion to its 
size, than the wings of a bird, nature herself has taught us that, 

In what proportion 301 . The resistance of a medium is 
is the resistance oj a 

medium t in exact proportion to its density. 


* A similar effect, but with a reversed action, is produced when ft long rope 
lightly strained between two points, is forcibly pulled in the middle 











NATURAL PHILOSOPHY 


<J8 


362. A body falling through water will move more slot\ ly than 
one falling in the air. because it meets with more resistance from 
the inertia of the water, on account of the greater density of tho 
water. 

What is a 363. A Vacuum. — A Vacuum is unoccu- 
Vacuum? pi e d space; that is, a space which contains 
absolutely nothing. 

364. From this definition of a vacuum, it appears that it does 
not mean a space which to our eyes appears empty. What we call 
an empty bottle is, in fact, full of air, or some other invisible fluid. 
If we sink an empty bottle in water or any other liquid, neither the 
water nor any other liquid can enter until some portion of the air is 
expelled. A small portion of water enters the bottle immersed, 
and the air issues in bubbles from the mouth of the bottle. Other 
portions of water then enter the bottle, expelling the air in similar 
manner, until the water entirely fills the bottle, and then the air 
bubbles cease to rise. 

365. From this statement of the meaning of the term “ a vacuum 

it will be seen that if a machine be worked in a vacuum (or, as it 
is more commonly expressed in Latin, “ in vacuo ”) its motion will 
be rendered easier, because the parts receive no resistance from a 
surrounding medium. 


What is F*-ic- 366. Friction. — Friction is the resistance 

toon, and how which bodies meet with in rubbing against 
many kinds of h th 
friction are 

there ? De- There are two kinds of friction, namely, 
scribe each. the rolling and the sliding friction. The 
rolling friction is caused by the rolling of a circular body. 

36T. The sliding friction is produced by the sliding or 
dragging of one surface over another. 


358 ; Friction is caused by the unevenness of the surfaces which 
come into contact.* It is diminished in proportion as the surfaces 
are smoothed and well polished. The sliding friction is overcome 
with more difficulty than the rolling. 


* All bodies, how well soever they may be polished, have inequalities ii 
their surfaces, which may be perceived by a microscope. When, therefore 
the surfaces of two bodies come into contact, the prominent parts of the 
ot 3© will often fall into the hollow parts of the other, and cause more or 
less resistance to motion. 


THE MECHANICAL TOWERS 


99 


iVhat portion 369. Friction destroys, but never can generate, 
a machine is^ motion ‘ is usually computed that friction 


lost by fric¬ 
tion 1 


destroys one-third of the power of a machine. 
In calculating the power of a machine, there¬ 
fore, an allowance of one-third must be made for loss by fric¬ 
tion.* 


What is used grease, black-lead or powdered soap- 

to lessen fric- stone, is used to lessen friction, because they act 
tionl and as a polish by filling up the cavities of the 

U ^' rubbing surfaces, and thus make them slide more 

easily over each other. 

How docs fric- 371. Friction increases: 

lion increase? (1.) As the weight or pressure is increased. 

(2.) As the extent of the surfaces in contact is increased 
(3.) As the roughness of the surface is increased. 

H.,W may fric- 372 - FiietioD “ a y bc diminished : 

lion be dimin- (1.) By lessening the weight of the body in 

motion. 

(2.) By nmclianically reducing the asperities of the sliding 
surfaces. 

(3.) By lessening the amount of surface of homogeneous 
bodies in contact with each other. 

(4.) By converting a sliding into a rolling motion. 

(5.) By applying some suitable unguent.t 


* When finely-polished iron is made to rub on bell-metal, the friction is 
said to be reduced to about one-eighth. Mr. Babbit, of Boston, has pre¬ 
pared a composition for the wheel-boxes of locomotive engines and other 
machinery, which, it is said, has still further reduced the amount of fric- 
t‘on. This composition is now much in use. As the friction between 
rolling bodies is much less than in those that drag, the axle of large wheels 
is sometimes made to move on small wheels or rollers. These are called 
friction wheels, or friction rollers. They turn round their own centre as 
the wheel continues its motion. 

f From the experiments made by Coulomb, it appears that the friction 
of heterogeneous ; bodies is generally less than that of homogenous that 
is, that if a body rub against another composed of the same kind of wood 
or metal, the friction is greater than that of different kinds of metal, or of 
weed. 

Ferguson’s experiments go to prove that the friction of polished steel 
against polished steel is greater than that of lolished steel on copper or on 


NATURAL PHILOSOPHY. 

373. Friction, although, it retards the motion 
of machines, and causes a great loss of power, 
performs important benefits in full compensation. 
Were there no friction, all bodies on the surface of the earth 
would be clashing against each other, Rivers would dash with 
unbounded velocity, and we should see little but motion and 
collision. ! But, whenever a body acquires a great velocity, it 
soon loses it by friction against the surface of the earth. 

374. The friction of water against the surfaces it runs over soon 
reduces the rapid torrent to a gentle stream ; the fury of the tempest 
is lessened by the friction of the air on the face of the earth ; and 
the violence of the ocean is soon subdued by the attrition of its own 
waters. Our garments, also, owe their strength to friction ; and 
die strength of ropes, cords, sails and various other things, depends 
on the same cause, for they are all made of short fibres pressed 
together by twisting, and this pressure causes a sufficient degree of 
friction to prevent the fibres sliding one upon another. Without 
friction it would be impossible to make a rope of the fibres of hemp, 
or a sheet of the fibres of flax; neither could the short fibres of 
cotton have ever been made into such an infinite variety of forms as 
they have received from the hands of ingenious workmen. Wool 
also, has been converted into a thousand textures of comfort and 
luxury, and all these are constituted of fibres united by friction. 

What is the 375. REGULATORS OF MOTION. — THE 
Pendulum ? Pendulum.— The Pendulum* consists of a 


100 

Whai me the 
uses of f ric¬ 
tion ? 


brass. In a combination where gun-metal rubs against steel, the same 
weight may be moved with a force of fifteen and a half pounds that it 
would require twenty-two pounds to move when east-iron moves against 
steel. 

* The pendulum was invented by Galileo, a great astronomer of Florence, 
in the beginning of the seventeenth century. Perceiving that the chan¬ 
deliers suspended from the ceiling of a lofty church vibrated long and with 
great uniformity, as they were moved by the wind or by any "accidental 
disturbance, he was led to inquire into the cause of their motion, and this 
inquiry led to the invention of the pendulum. From a like apparently 
insignificant circumstance arose the great discovery of the principle of 
gravitation. During the prevalence of the plague, in the year 1065, Sir 
Isaac Newton retired into the country to avoid the contagion. Sitting in 
his orchard, one day, he observed an apple fall from a tree. His inquisitive 
mind was immediately led to consider the cause which brought the apple 
to the ground, and the result of his inquiry was the discovery of that grand 
principle of gravitation which may be considered as the first and most im¬ 
portant law of material nature. Thus, out of what had been before the 
eyes of men, in one shape or another, from the creation of the world, did 
these pniloa >pkers bring the most important results. 


REGULATORS OF MOTION. 


101 


weight or ball suspended by a rod, and made to swing 
backwards and forwards. 


What are the 

motions of a 376. The motions of a pendulum are called 

V ( and'hoiv^~ Orations or oscillations, and they are 

jre they caused by gravity.* 

zaused ? 


The part of a circle through wliLv it moves 
is called its arc . 

877. The vibrations of pendulums of equal 

"theliine'oj the length are very nearly equal, whether they 

vibrations of move through a greater or lest part of thcii 
pendulums of , 

equal length ? aics *T 


What is the 
arc of a pend¬ 
ulum ? 


What differ- 

c^\ro ic tliooro iti 


378. In Fig. 57 AB represents a pendulum. fig. 57. 

D F E C the arc in which it vibrates. If the ° 8 ' a A 
pendulum be raised to E it will return to F, if it 
be raised to C it will return to D, in nearly the d 
same length of time, because that, in proportion ^ ^ i 
as the arc is more extended, the steeper will be 
its beginnings and endings, and, therefore, the more rapidly 
will it fall.I 



* When a pendulum is raised from a perpendicular position, its weight 
will cause it to fall, and, in the act of falling, it acquires a degree of motion 
which impels it to a height beyond the perpendicular almost as great -is 
that to which it was raised. Its motion being thus spent, gravity again 
acts upon it to bring it to its original perpendicular position, and it again 
acquires an impetus in falling which carries it nearly as high on the oppo¬ 
site side. It thus continues to swing backwards and forwards, until the 
resistance of the air wholly arrests its motion. 

It will be understood that gravity affects every part of the length of the 
pendulum. A ball or llattened weight is attached to the lower end of the 
pendulum to concentrate the effects of gravity in a single point. 

In the construction of clocks, an apparatus connected with the weight or 
the spring is made to act on the pendulum with such a force as to enable it 
to overcome the resistance of the air, and keep up a continued motion. 

f It has already been stated that a body takes the same time in rising 
and falling when projected upwards. Gravity brings the pendulum dowu, 
and inertia causes it to continue its motion upwards. 

J The length of the arc in which a pendulum oscillates is called its 
amplitude. 


9* 



102 


NATURAL PHILOSOPHY 


On what does 379. The time occupied in the vibration of 

the time f the a pendulum depends upon its length. The 
oscillations of 1 . . 

u pendulum longer the pendulum, the slower are its vi- 

depend ? brations. * 


380. The length of a pendulum which 
vibrates sixty times in a minute (or, in other 
words, which vibrates seconds) is about thirty- 
nine inches. But in different parts of the 
earth this length must be varied. 

Which must be the ^ pendulum, to vibrate seconds at the 
longer , to vibrate r 7 

seconds , a pendulum equator, must be shorter than one which 

at the equator or one v ibrates seconds at the poles, j* 
it the poles f * 1 

Row is a clock 381. A clock is regulated by lengthening 

'emulated ? or shortening the pendulum. By lengthening 

the pendulum, the clock is made to go slower; by shortening 

it, it will go faster. J 


What is the 
length of a 
'pendulum that 
vibrates once 
every second 
of time ? 


* The weight of the ball at the end of a pendulum .does not affect the 
duration of its oscillations. 

f The equatorial diameter of the earth exceeds the polar diameter by 
about twenty-six miles ; consequently the poles must be nearer to the centre 
of the earth’s attraction than the equator, and gravity must also operate 
with greater force at the poles than at the equator. Hence, also, the length 
of a pendulum, to vibrate in any given time, must vary with the latitude 
of the place. 

.J: The pendulum of a clock is made longer or shorter by means of a screw 
beneath the weight or ball of the pendulum. The clock itself is nothing 
more than a pendulum connected with wheel-work, so as to record the 
number of vibrations. A weight is attached in order to counteract the 
retarding effect of friction and the resistance of the air. The wheels show 
how many swings or beats of the pendulum have taken place in a given 
time, because at every bgat the tooth of a wheel is allowed to pass. Now, 
if this wheel have sixty teeth, it will turn round once in sixty vibrations 
of the pendulum, or in sixty seconds ; and a hand, fixed on the axis of the 
wheel projecting through the dial-plate, will be the second-hand of the 
clock. Other wheels are so connected with the first, and the number of 
teeth in them is so proportioned, that the second wheel turns sixty times 
slower than the first, and to this is attached the minute-hand ; and the 
third wheel, moving twelve times slower than the second, carries the hour- 
hand. On account of the expansion of the pendulum by heat, and its con¬ 
traction by cold, clocks will go slower in summer than in winter, became 
the pendulum is thereby lengthened at that season. 


RliGULATOKfcj OF MOTION. 


lua 

H what pro- 330 The lengths of pendulums are to each 

portion are the . 0 , 

lengths of other as the square of the time of their 

pendulums ? vibration. 

£83. According to this law, a pendulum, to vibrate once in two 
♦econds, must be four times as long as one that vibrates once in one 
v>ocond ; to vibrate once in three seconds, it must be nine times as 
long; to vibrate once in four seconds, it must be sixteen times as 
long ; once in five seconds, twenty-five times as long, &c. 

The. seconds employed in the vibrations being 
1, 2,3,4, 5, 6,7,8, 9, 
me length of the pendulums would be as 

1, 4, 9, 16, 25, 36, 49 64, 81. 

A pendulum, therefore, to vibrate once in five seconds , must be 
over eighty feet in length. 

384. As the oscillations of a pendulum are dependent upon gravi¬ 
tation, the instrument becomes useful in ascertaining the force of 
gravity at different distances from the centre of the earth. 

385. It has already been stated that the centrifugal force at the 
equator is greater than in those parts of the earth which are near 
the poles. As the centrifugal force operates in opposition to that 
of gravity , it follows that the pendulum must also be affected by it; 
and this affords additional reason why a pendulum, to vibrate 
seconds at the equator, must be shorter than one at the poles. It 
has been estimated that, if tht revolution of the earth around its 
axis were seventeen times faster than it is, the centrifugal force at 
the equator would be equal to the force of gravity, and, conse¬ 
quently, nei ther could a pendulum vibrate, nor would bodies them 
have any weight. 

386. As every part of a pendulum-rod tends to vibrate in a dif¬ 
ferent time, at is necessary that all pendulums should have a weight- 
attached to them, which, by its inertia, shall concentrate the attract¬ 
ive force of gravity. 

387. Pendulums are subject to variation in warm and cold 
weather, on account of the dilatation and contraction of the mate¬ 
rials of which the rod is composed, by heat and cold. For this 
reason, the same pendulum is always longer in summer than it is in 
winter; and a clock will, therefore, always be slower in summer 
than in winter, unless some means are employed by which the 
effects of heat and cold on the length of the pendulum can be coun¬ 
teracted. This .is sometimes effected in what is called the gridiron 
pendulum by combining bars or rods of steel and brass, and in the 
mercurial penlulum by enclosing a quantity of quicksilver in a 
tube near the bottom of the pendulum. 

388. In order to secure a continuous motion to the pendulum 
(or, in other w-axls, to keep a clock in motion), it is necessary that 
the pendulum * iould hang in a proper position. A practised ear 
can easily detev any error in this respect by the irregularity in the 


104 


NATURAL PHILOSOPHY. 


ticking, or (as it is called) by its being “ out of beat .” To remedy 
this fault, it is necessary either to incline the clock to the one side 
or the other, until the tickings are synchronous ; or, in other words, 
are made at equal intervals of time. It can sometimes be done 
without moving the clock, by slightly bending the upper appendage 
of the pendulum in such a manner that the two teeth, or pro¬ 
jections, shall properly articulate with the escapement-wheel. [*Sc5 
No. 303.] 


* 189 . Table of the Lengths of Pendulums to vibrate Seconds in different latitudes 



Inches. 



Inches 

At the equator, 

39. 

At the equator, 

39. 

Lat. 10° North, 

39.01 

Lat. 10° 

bouth, 

39.02 

20 “ 

39.04 

20 

it 

39.04 

30 “ 

39.07 

30 

a 

39.07 

40 “ 

39.10 

40 

(< 

39.10 

50 “ 

39.13 

50 

a 

39.13 

60 “ 

39.16 

60 

a 



390. The observations have been extended but little further, north 
or south of the equator. Different observers have arrived at different 
results ; probably on account of their different positions in relation 
to the level of the sea in which the observations were made. In 
such a work as this, a table of this kind, without pretending to ex¬ 
treme accuracy, is useful, as show ; ng that theory has been con¬ 
firmed by observation. 

391. The moving power of a clock is a weight, which, being wound 
up, makes a constant effort to descend, and is prevented by a small 
appendage of the pendulum, furnished with two teeth, or projec¬ 
tions, which the vibrations of the pendulum cause alternately to 
fall between the teeth of a wheel called the escapement-wheel. 
The escapement-wheel is thus permitted to turn slowly, one tooth 
at a time, as the pendulum vibrates. If the pendulum with its 
appendage be removed from the clock, the weight will descend very 
rapidly, causing all the wheels to revolve with great velocity, and 
the clock becomes useless as a time-piece. 

392. The moving power of a watch* is aspring, called the main¬ 
spring, which being tightly wound around a central pin, or axis, its 
elasticity makes a constant effort to loosen. This power is commu¬ 
nicated to a balance-wheel, acted upon by a hair-spring, and having 
an escapement similar to that of the clock. If the hair-spring, with 
the escapement, be removed, the main-spring, being unrestrained, * 


* A watch differs from a clock in having a vibrating wheel, instead of a 
pendulum. This wheel is moved by a spring, called the hairspring. Thf 
place of the weight is supplied by another larger spring, called the main 
spring . 


REGULATORS OF MOTION. 


I Ob 


mil cause the wheels to revolve with great rapidity, ana the watch, 
also, becomes useless as a time-piece.* 

What is a Bat- 393. The Battering Ram.—T ho Battering 
ter ing Ram? -r» 6 

liam was a military engine of great power, used 

to beat down the walls of besieged places. 

Explain 394. Its construction, and the principle on which it 
H^.58. was worked, may be understood by inspection of Fig 
58, in which A B represents a large beam, heavily loaded, with 

Fig. 58. 



a nead of iron, A, resembling the head of a ram, from winch it 
takes its name. The beam is accurately balanced, and su.** 
pended by a rope or chain C, hanging from another beam, sup¬ 
ported by the frame D E F G\ At the extreme end B, ropes 
or chains were attached, by,which it could be drawn upwards 
through the arc of a circle, like a pendulum. The frame was 
sometimes mounted on wheels. 


395. Battering rams were frequently from fifty to a hundred 

feet in length, and, moving with a force compounded of their 

weight and velocity, were almost irresistible.! 

* As a regulator of motion, the pendulum of tho clock is to be length 
vied or shortened, and the hair-spring of a watch is to be tightened or 
loosened. This is to be done in the former case in the manner already 
explained in the text; in the latter, by turning what is called the regu¬ 
lator, which tightens or loosens the hair-spring. 

i The ram used by Demetrius Polioroetes at the siege of Rhodes wii« 


































106 


NATURAL PHILOSOPHY. 


0%. The force of a battering ram is estimated by Its momentum 
chat is its weight multiplied by its velocity. 

397. Questions for Solution. 

(1.) Suppose a battering ram weighing 57(10 lbs., with a velocity of 11 
feet in a second, could penetrate a wall, with what velocity must a can¬ 
non-ball weighing 24 lbs. move to do the same execution 7 

5700 X 11 = 03300 -f- 24 — 2040 feet, or one half of a mile in a second 
(2.) If a battering ram have a momentum of 58,000 and a velocity of 8. 
what is its weight 7 Ans. 7250 

(3.) If a ram have a weight of 90,000 and a momentum 81,000, what is 
its velocity 7 Ans. .9 

(4.) What is the weight of a ram with a velocity of 12 and a momentum 
60,000 ? Ans. 5000. 

(5.) Will a cannon-ball of 9 lbs. and a velocity of 3,000, or a ram with a weight of 
15,000 and a velocity of 2, move with the greater force? Ans. The ram. 

What is the 898. The Governor. — The Governor is an 

Governor J . . c i • , . 

ingenious piece or mechanism, constructed on 

the principle of the centrifugal force, by means of .which 

the supply of power in machinery is regulated.* 

399. Fig. 59 represents a governor. A B and 
A C are -two levers, or arms, loaded with heavy 

one hundred and six feet long. At the siege of Jerusalem Vespasian em¬ 
ployed a ram fifty feet long, armed with an iron butt, with twenty-five pro¬ 
jecting points, two feet apart, each as thick as the body of a man. The 
counter weight at the hindmost end amounted to 1075 cwt., and 1500 men 
were v equired to work the machine. 

* his very useful appendage to machinery, though long used in mills 
and other mechanical arrangements, owes its happy adaptation to the steam 
engine to the ingenuity of Mr. James Watt. 

In manufactures, there is one certain and determinate velocity with 
which the machinery should be moved, and which, if increased or dimin¬ 
ished, would render the machine unfit to perform the work it is designed to 
execute. Now, it frequently happens that the resistance is increased or 
liminisbed by some of the machines which are worked being stopped, or 
others put on. The moving power, having this alteration in the resistance, 
would impart a greater or less velocity to the machinery, were it not for 
the regulating power of the govenior, which increases or diminishes the 
supply of water or of steam, which is the moving power. 

liut, besides the alteration in the resistance just noticed, there is, also, 
frequently, greater changes in the power. The heat by which steam is 
generated cannot always be perfectly regulated. At times it may afford an 
exeess, and at other times too little expansive power to the steam. Water, 
also, is subject to change of level, and to consequent alteration as a moving 
power. The wind, too, which impels the sails of a wind-mill, is subject to 
great increase and diminution. To remedy all these inconveniences is the 
ih’ty assigned to the governor. 


Explain 

Fig. 59. 



KEGULATOftS (. F MOTION. 


1U? 



balls at their extremities B and C, and 
suspended by a joint at A upon the ex¬ 
tremity of a revolving shaft AD. A 
a is a collar, or sliding box, connected 
with the levers by the rods b a and c a. 
with joints at their extremities. When 
the shaft A D revolves rapidly, the cen¬ 
trifugal force of the balls B and C will 
cause them to diverge in their attempt to 
fly off, and thus raise the collar by means 
of the rods b a and c a. On +he con¬ 
trary, when the shaft A D revolves slowly, the weights B and 
C will fall by their own weight, and the rods b a and c a will 
cause the collar a to descend. The steam-valve in a steam- 
engine, or the sluice-gate of a water-wheel, being connected 
with the collar a, the supply of steam or water, which puts the 
works in motion, is thus regulated. 

What is the 400. Main-spring of a watch consists of a 
Main-spring long ribbon of steel, closely coiled, and contained 
a watch ? i n a roun d box. it is employed instead of a 
weight, to keep up the motion. 

401. As the spring, when closely coiled, exerts a stronger force 
than when it is partly loosened, in order to correct this inequality 
the chain through which it acts is wound upon an axis surrounded 
by a spiral groove (called a fusee), gradually increasing in diameter 
from the top to the bottom ; so that, in proportion as the strength 
of the spring is diminished, it may act on a larger lever, or a larger 
wheel and axle. 


Explain 
Fig. 60. 


402. Fig. 60 represents a spring coiled m a round box 
A B is the fusee, FiK 60t 

A 

JL 


surrounded by a spiral groove, 
on which the chain C is wound. 
When the watch is recently 
wound, the spring is in the 
greatest state of tension, ana 
will, therefore, turn the fusee 





















NATURAL r«fLi>SOPHY. 


I OH 

by the smallest groove, on the principle of the wheel and A,xie 
As the spring loses its force by being partly unwound, i. act* 
upon the larger circles of the fusee ; and the want of sti ;ngth 
in the spring is compensated by the mechanical aid of a larger 
wheel and axle in the larger grooves. By this means the 
spring is made at all times to exert an equal power upon the 
fusee. The motion is communicated from the fusee by a cogged 
wheel, which turns with the fusee. 

403. Hydrostatics.* —Hydrostatics treats 
of the nature, gravity and pressure of fluids 

404. Hydrostatics is generally confined to the 
consideration of fluids at rest, and Hydraulics to 
fluids in motion. 

405. A Fluid is a substance which yields to 
the slightest pressure, and the particles of 

which, having but a slight degree of cohesion, move easily 
among themselves.j* 


Of what does 
Hydrostatics 
treat 1 

What is the 
difference be¬ 
tween Hy¬ 
draulics and 
Hydrostatics ? 

What is a 
Fluid ? 


* The suijects of Hydraulics and Hydrostatics are sometimes descrioed 
under the general name of Hydrodynamics. The three terms are from the 
Greek language, compounded of vdwg ( hudor ), signifying water, and Svrayig 
(dunamis), force or power ; orarixog (staticos), standing, and u.vXoc ( aulos ), a 
tube or pipe. Hence Hydrodynamics would imply, the science which treats 
of the properties and relations of water and other fluids, whether in a state 
of motion or rest ; while the term Hydrostatics would be confined to the 
consideration of fluids in a state of rest, and Hydraulics to fluids in motion 
through tubes or channels, natural or artificial. 

f There is this remarkable difference between bodies in a fluid and 
bodies in a solid form, namely, that every particle of a fluid is perfectly 
independent of every other particle. They do not cohere in masses, like 
the particles of a solid, nor do they repel one another, as is the case with the 
particles composing a gas. They can move among one another with the 
least degree of friction,. and, when they press down upon one another in 
virtue of their own weight, the downward pressure is communicated in aU 
directions, causing a pressure upwards, sideways, and in every possible 
manner. Herein the particles of a fluid differ from the particles'of a solid, 
even when reduced to the most impalpable powder; and this it is which con 
sf itutes fluidity, namely, the power of transmitting pressure in every direction , 
and that , too, ivith the least degree of friction. The particles whioh compose 
a fluid must be very much smaller than the finest grain ox an 'in. palpable 
yowder. 


til \ ,DiiUSTAT j US. 


lU ( J 


How does a 40o. A. liquid differs from a fluid in its 
liquid differ degree of compressibility and elasticity. Fluids 
fi°m a fluid are hjghjy compressible and elastic. Liquids, 
on the contrary, have but a sh'ght degree either of com- 
possibility or of elasticity.* 

407. Another difference between a liquid and a fluid arises fr( in 
the propensity which fluids have to expand whenever all external 
pressure is removed. Thus, whenever a portion of air or gas is 
removed from a closed vessel, the remaining portion will expand, 
and, in a rarer state, will fill the whole vessel. Liquids, on the 
contrary, will not expand without a change of temperature. Liquids, 
also, have a slight degree of cohesion , in virtue of which the par¬ 
ticles will form themselves into drops ; but the particles of fluids 
seem to possess the opposite quality of repulsion , which causes 
them to expand without limit, unless confined within the bounds of 
some vessel, or restricted within a certain bulk by external pressure. 

408. The fluid form of bodies seems to be in great measure, if 
not wholly, attributed to heat. This subtle agent insinuates itself 
between the particles of bodies, and forces them asunder. Thus, 
for instance, water divested of its heat becomes ice," which is a 
solid. In the form of water it is a liquid, having but in a very 
slight degree the properties either of compressibility or elasticity. 
An additional supply of heat converts it into steam, endowed with 
a very great degree both of elasticity and compressibility. But, so 
soon as steam loses its heat, it is again converted into water. 
Again, the metals become liquid when raised to certain tempera¬ 
tures, and it is known that many, and supposed that all, of them 
would be volatilized if the required supply of heat were applied. 


* The celebrated experiment made at Florence, many years ago, to test 
the compressibility of water, led to the conclusion that water is wholly 
incompressible. Later experiments have proved that it may be com¬ 
pressed, and that it also has a slight degree of elasticity. In a voyage to 
the West Indies, in the year 1839, an experiment was made, at the sugges¬ 
tion of the author, with a bottle filled with fresh water from the tanks on 
the deck of the Sea Eagle. It was hermetically sealed, and let down to the 
depth of about seven hundred feet. On drawing it up, the bottle was still 
full, but the water was brackish, proving that the pressure at that great 
depth had forced a portion of the deep salt water into the bottle, previously 
compressing the water in the bottle to make room for it. As it rose to the 
surface, its elasticity restored it to its normal state of density. 

At great depths in the sea the pressure of the superincumbent mass 
increases the density by compression, and it has been calculated that, at a 
depth of about ninety miles, water would be compressed into one-half of its 
volume, and at a depth of 360 miles its density would be nearly equal to 
that of mercury. Under a pressure of 15,000 lbs. to a square inch, Air 
Perkins, of Newburyport, subsequently of London, has sh . wn that water h 
reduced in bulk one part in twenty-four. 

10 


% 


10 


NATURAL PHILOSOPHY. 


The science of Geology furnishes ■sufficient reasons lor believing 
that all known substances were once not only in the liquid form, 
but also previously existed in the form of gas.* 


Ho w do fluids 409. Gravitation of Fluids. — Fluids gravi- 

gravitate! tute in a more perfect manner than solids, on 
account of their want of cohesive attraction. The particles of a 
solid body cohere so strongly that, when the centre of gravity 
is supported, the whole mass will be supported. But every 
■particle of a fluid gravitates independently of every other par - 
tide. 


Tx „ , 410. On account of the independent gravita- 

W'hy cannot A c 

fluids be tion and want of cohesion of the particles ot a 

moulded into fluid, they cannot be formed into figures, nor pre- 
fi a ures. served in heaps. Every particle makes an effort 

to descend, and to preserve what is called the level or equi¬ 
librium. 

What is the 411. The level or equilibrium of fluids is 
equilibrium of the tendency of the particles so to arrange 
fluuls l themselves that every part of the surface 

shall be equally distant from the centre of the earth ; that 
is, from the point towards which gravity tends. 


What is the 412. Hence the surface of all fluids, when in a 
^surface o} e all s ^ e res ^» P ar takes the spherical form of the 
fluids / earth. 


413. For the same reason, a fluid immediately conforms itself tc» 
the shape of the vessel in which it is contained. The particles of a 
solid body being united by cohesive attraction, if any one of them, 
be supported it will uphold those also with which it is united. 
But, when any particle of a fluid is unsupported, it is attracted 
down to the level of the surfaqp of the fluid; and the readiness with 
which fluids yield to the slightest pressure will enable the particle, 
>y its own weight, to penetrate the surface of the fluid, and mis 
vith it. 


* The science of Chemistry unfolds the fact that all the great changes in 
the constitution of bodies are accompanied by the exhibition of heat either 
■u a free or latent condition. 


11Y DKOSTAT1CS. 


11J 


What is Ca- 414. CAPILLARY ATTRACTION. — Capillary 

pillary Aitrao Attraction i s that attraction which causes 
tion ? 

What are Ca - fluids to ascend above their level in capillary 
fillary Tubes ? tubes. Capillary * tubes are tubes with very 
fine bore. 

415. This kind of attraction exhibits itself not only in tubes, but 
also between surfaces which are very near together. This may be 
beautifully illustrated by the following experiment. Take two 
pieces of flat glass, and, having previously wet them, separate their 
edges on one side by a thin strip of wood, card or other material; 
tie them together, and partly immerse them perpendicularly in 
colored water. The water will then rise the highest on that side 
vhere the edges of the glass meet, forming a beautiful curve down¬ 
wards towards the edges which are separated by the card. 

416. Immerse a number of tubes with fine bores in a glass of 
colored water, and the water will rise above its equilibrium in all, 
but highest in the tube with the finest bore. 

417. The cause of this seems to be nothing more than the ordi¬ 
nary attraction of the particles of matter for each other. The sides 
of a small oiifice are so near to each other as to attract the particles 
of the fluid on their opposite sides, and, as all attraction is strongest 
in the direction of the greatest quantity of matter, the water is 
raised upwards, or in the direction of the length of the tube. On 
the outside of the tube, the opposite surfaces cannot act on the 
same column of water, and, therefore, the influence of attraction is 
here imperceptible in raising the fluid. 

418. All porous substances, such as sponge, bread, linen, sugar, 
&c., may be considered as collections of capillary tubes; and, for 
this reason, water and other liquids will rise in them when they are 
partly immersed. 

419. It is on the same principle that the wick of a lamp w r ill 
carry up the oil iO supply the flame, although the flame is several 
inches above the level of the oil.f If the end of a towel happen to 

* The word capillary is derived from the Latin word capilla (hair), and it 
Is applied to this kind of attraction because it is exhibited most prominently 
in tubes the bores of which are as fine as a hair, and hence called capillary 
tubes. 

-f The reason why well-filled lamps will sometimes fail to give light is, 
that the wick is too large for its tube, and, being thus compressed, the 
japillary attraction is impeded by the compression. The remedy is to 
reduce the size of the wick. Another cause, also, that prevents a clear 
tight, is that the flame is too far from the surface of the oil. As capillary 
ittraction acts only at short distances, the surface of the oil should always 
te within a short distance of the flame. But another reason, which requires 
particular attention, is, that all kinds of oil usually employed for lamps 
iontain a glutinous matter, of which no treatment can wholly divest them, 
riiis matter tills the poies or capillary tubes of the wick, aud prevents t'*f 


NATURAL PHILOSOPHY. 


m 


be left in a basin of water, jt will, empty the basin of its contents 
On the same principle, when a dry wedge of wood is diiven inti 
the crevice of a rock, as the rain falls upon it, it will absorb the 
water, swell, and sometimes split the rock. In this manner mill¬ 
stone quarries are worked in Germany. 

420. Endosmose and Exosmose. —In addition to the capillary 
attraction just noticed as peculiar to fluids, another may be men¬ 
tioned, as yet but imperfectly understood, wdiich seems to be due 
partly to capillary and partly to chemical attraction, known under 
the names endosmose and exosmose * These phenomena are mani¬ 
fested in the transmission of thin fluids, vapor and gaseous matter, 
through membranes and porous substances. The ascent of the sap 
in vegetable, and the absorption of nutritive matter by the organs 
of animal life, are to be ascribed to these causes. 

421. When two liquids of different densities are separated by a 
membranous substance or by porcelain unglazed, endosrnos* will 
carry a current inwards , and exosmose will force one outwards , thus 
causing a partial mixture of the fluids. 


422. Experiment. — Take a glass tube, and, tying a piece of bladder oj 
clean leather over one end for a bottom, put some sugar into it, and haying 
poured a little water on the sugar, let it stand a few hours in a tumbler of 
water. It will then be found that the water has risen in the tube through 
the membranous substance. This is due to endosmose. If allowed to stand 
several days, the liquid will rise several feet. 

If the experiment be reversed, and pure water be put into the tube, and 
the moistened sugar into the tumbler, the tube will bo emptied by exosmose. 

423. The liquid that has the less density will generally pass to the 
denser liquid and dilute it. 


What peculi- 424. Gravitation of Fluids of different 
arity is there Densities. — When solid bodies are placed one 
Nation of fluids a ^ ove an °ther, they will remain in the position in 
of different which they are placed so long as their respective 
densities ? centres of gravity are supported, without regard 
to their specific gravity. With fluids the case is different. 


ascent of the oil to feed the flame. For this reason, the wicks of lamps 
should be often renewed. A wick that has been long standing in a lamp 
will rarely afford a clear and bright light. Another thing to be noticed by 
those who wish the lamp to perform its duty in the best possible manner 
is, that the wick be not of such size as, by its length, as well as its thickness, 
to fill the cup, and thereby leave no room for the oil. It must also bo 
remembered that, although the wick when first adjusted may be of the 
proper size, the glutinous matter of the oil, filling its capillary tubes, causes 
the wick to swell, and thereby become too large for the tube, producing the 
tame difficulty as has ah’cady been noticed in cases where the wick is too 
large to allow the free operation of capillary attraction, 

* Endosmose, from ckW, within , and wopog, impulsion. Exo*mose, from 
c£, outwa j :l, and wopiog, impulsion 


HYDROSTATICS. 


113 


Fluids of toflerent specific gravity will arrange themselves in 
the order of their density, each preserving its own equilibrium. 

425. Thus, if a quantity of mercury, water, oil and air, be put 
into the same vessel, they will arrange themselves in the order of 
their specific gravity. The mercury will sink to the bottom, the 
water will stand above the mercury, the oil above the water, and 
the air above the oil; and the surface of each fluid will partake of 
the spherical form of the earth, to which they all respectively 
gravitate. 

vVhat is a Spirit 426 - A Water or Spirit Level is an in- 
Level, or Water strument constructed on the principle of the 
equilibrium of fluids. It consists of a glass 
tube, partly filled with w r ater, and closed at both ends. 
When the tube is not perfectly horizontal,— that is, if one 
end of the tube be lower than the other,— the water will 
run to the lower end. By this means the level of any line 
to which the instrument is applied may be ascertained. 


A B 


is a 


1 %. 61 
A C B 


427. Fig. 61 represents a Water Level. 
gl ass tube partly filled vrith water. 

C is a bubble of air occupying the 
space not filled by the water. When both 
ends of the tube are on a level, the air-bubble 
will remain in the centre of the tube; but, if either end of the. 
tube be depressed, the water will descend and the air-bubble 
will rise. The glass tube, when used, is generally set in a woode" 
or a brass box. It is an instrument much used by carpersiert 
masons, surveyors, &c. 

[N. B. The tube is generally filled with spirit, instead of water, o» 
account of the danger that the water will freeze aod burst the glass, llenct 
the instrument is called indifferently the Spirit Level or the Water Level.] 

428. Effect of the Peculiar Gravitation 
fli!ids°do lh less 0F Fluids. — Solid bodies gravitate in masses, 
damage than their parts being so connected as to form a 
falling solids l w h 0 le, and their weight may be regarded as 
concentrated in a point, called the centre of gravity; while each 
10 * 




IL4 


NATURAL PHILOSOPHY. 


particle if a fluid may be considered as a separate mass, gravi¬ 
tating independently. 

It is for this reason that a body of water, in falling, does 
less injury than a solid body of the same weight. But, if the 
water be converted into ice, the particles losing their fluid form, 
and being united by cohesive attraction, gravitate unitedly in 
one mass. 


In what direc- 40 Q PreSSURE OF FLUIDS. — Fluids not 
tion do fluids 

press, on ac - only press downwards like solias, but also 

count of their upwaiN } 3 sidewise * and in every direction. 
weight ? r 1 1 

430. So long as the equality of pressure is undisturbed, every 
particle will remain at resv. If the fluid be disturbed by agitating 
it, the equality of pressuie will be disturbed, and the fluid will not 
rest until the equilibrium b restored. 


How are the 431. The downward pressure of fluids is 
downward , lat- shown by making an aperture in the bottom of 
eral and up - a vesse i 0 f water. Every particle of the fluid 
J Iffluidfshown ? above the aperture will run downwards through 
the opening. 

432. The lateral pressure is shown by making the aperture 
at the side of the vessel. The fluid will then escape through 
the aperture at the side. 

433. The upward pressure is shown by taking a glass tube, 
open at both ends, inserting a cork in one end (or stopping it 
with the finger), and immersing the other in the water. The 
water will not rise in the tube. But the moment the cork is 
taken out (or the finger removed), the fluid will rise in the tube 
to a level with the surrounding water. 


Fig. 62. * If the particles of fluids were arranged in 

Fig. 63. regillar columns, as in Fig. 62, there would be 
no lateral pressure ; for when one particle is per¬ 
pendicularly above the other, it can press only 
downwards. But, if the particles be arranged aa 
in Fig. 63, where a particle presses between tw« 
particles beneath, these last must suffer a lateral pressure. In whatever 
manner the particles are arranged, if they be globular, as is supposed, there 
must bo spaces between them f See Fig. 1 ypage 22 .] 



& 


HYDROSTATICS. 


116 


What i. the 434. The pressure of a fluid is in propor* 

i°w oj fluid tion to the perpendicular distance from the 
vressure i . 

^* surface; that is, the deeper the fluid, the 

greater will be the pressure. This pressure is exerted in 

every direction, so that all the parts at the same depth 

Dress each other with equal force. 

435. A bladder, filled with air, being immersed in water, will 
Se contracted in size, on account of the pressure of the water in all 
iirections; and the deeper it is immersed, the more will it be con¬ 
tacted.^ 

436. An empty bottle, being corked, and, by means of a weight, 
iet down to a certain depth in the sea, will either be broken by the 
pressure, or the cork will be driven into it, and the bottle be filled 
with water. This will take place even if the cork be secured with 
wire and sealed. But a bottle filled with water, or any other liquid, 
may be iet down to any depth -without damage, because, in this 
case, the internal pressure is equal to the external.f 


* The weight of a cubic inch of water at the temperature of 62o of Fah¬ 
renheit's thermometer is 36066 millionths of a pound avoirdupois. The 
pressure of a column of water of the height of one foot will therefore bo 
twelve times this quantity, or .4328 (making allowance for the repeating 
decimal), and the pressure upon a square foot by a column one foot high 
will be found by multiplying this last quantity by 144, the number of 
square inches in a square foot, and is therefore 62.3332 
Hence, at the depth of 

lbs. lbs. 


I foot the pressure on a square 

inch is 4328, on 

a square foot, 

62.3232 

2 feet . 

. . . 8656, “ 

(( 

(( 

124.6464 

3 “ . 


it 

tt 

186.9696 

4 “ . 

. . . 1.7312, « 

it 

tt 

249.2928 

5 “ . 


tt 

tt 

311.6160 

6 “ . 

, . . 2.5968, “ 

a 

tt 

373.9392 

7 “ . 

„ 3.0296, « 

tt 

tt 

436.2624 

8 “ . 

. . , 3.4624, “ 

tt 

it 

498.5856 

9 “ . 

. . . 3.8952, “ 

a 

tt 

560.9088 

10 “ . 

. . . 4.3280, « 

a 

it 

623.2320 

J00“ . 


tt 

it 

6232.3200 

From this table, the pressure 

on any eui ^ace at any depth may easily be 


found. 

It will thus be seen that there is a certain limit beyond which divers 
cannot plunge with impunity, nor fishes of any kind live. Wood that has 
been sunk to great depths in the sea will have its pores so filled with 
water, and its specific gravity so increased, that it will no longer float. 

f “Experiments at Sea .— We are indebted to a friend, who has just arrived 
fro?n Europe, says the Baltimore Gazette , for the fol'owing experiment? 
made ou board the Charlemagne : 

•- 26th of September, 1836, tlio weather being calm l corked an einptj 

















nt> 


NATURAL PHILOSOPHIC. 


437. Questions for Solution. 

(1.) What pressure is sustained by the body of a £<h having a surfaoe of 
9 square feet at the depth of 150 feet 1 Ans. 84136.32 lb. 

(2.) What is the pressure on a square yard of the banks of a canal, at the 
depth of four feet ? Ans. 2243.6352 lb. 

(3.) What pressure is exerted on the body of a man, at the depth of 
30 feet, supposing the surface of his body to be 2* sq. ydA Ans. 42068.16 lb. 

(4.) Suppose a whale to be at the depth of 200 feet, and that his body 
presents a surface of 150 yards. What is the pressure? Ans. 16827264 lb. 

(5.) How deep may a glass vessel containing 18 inches of square surface 
be sunk without being broken, supposing it capable of resisting an equal 
pressure of 1500 lbs.] Ans. 192.54/?.+ 

(6.) What is the pressure sustained on the sides of a cubical water-tight 
box at the depth of 150 feet below the surface, supposing the box to rest on 
f he bed of the sea, and each side to be 8 feet square? Ans. 299151.36 lb. 

(7.) How deep can a glass vessel bo sunk without breaking, sr •' posing 
that it be capable of resisting a pressure of 200 pounds on a square inch { 

Ans. 462.1/?. + 

' 438. The lateral pressure of a fluid proceeds 
11 hut causes the ei +irely from the pressure downwards, or, in 

lo/cTcil pressure " A 

0 f fi u i ( i s ? other words, from the weight of the liquid 

above; consequently, the lower an orifice is 
made in a vessel containing water or any other liquid, the 
greater will be the force and velocity with which the liquid will 
rush out. 


wine-bottle, and tied a piece of linen over the cork ; 1 then sank it into 
the sea six hundred*feet ; when drawn immediately up again, the cork waf 
inside, the linen remained as it was placed, and the bottle was filled with 
water. 

“ I next made a noose of strong twine around the bottom of the cork, 
which I forced into the empty bottle, lashed the twine securely to the neclr 
of the bottle, and sank the bottle six hundred feet. Upon drawing it up 
immediately, the cork was found inside, having forced its way by the twine, 
and in so doing had broken itself in two pieces ; the bottle was filled with 
water. 

“ I then made a stopper of white pine, long enough to reach to the bot¬ 
tom of the bottle; after forcing this stopper into the bottle, I cut it off about 
half an inch above the top of the bottle, and drove two wedges, of the same 
wood, into the stopper. I sank it six hundred feet, and upon drawing it 
up immediately the stopper remained as I placed it, and there was about 
a gill of water in the bottle, which remained unbroken. The water must 
have forced its way through the pores of the wooden stopper, although 
wedged as aforesaid ; and had the bottle remained sunk long enough, thexe 
is no doubt that it would have been filled with water.” [See also note on 
page 109.] 

It is the opinion of some philosophers that the pressure at very great 
depths the sea is so great that the water is condensed into a solid state; 
tud that at or near the centre of the earth, if the fluid could extend so 
deeply, this pressure would convert the whole into a solid mass of fire 


HYDROSTATICS. 


117 


Fig. 64. 



439 Fig. 64 represents a vessel of water, with ori- 
fi!r G 4 * ^ ces at the side at different dis¬ 
tances from the surface. The 
different curves in the figure, described by 
the liquid in running out of the vessel, show 
the action of gravity, and the effects pro¬ 
duced by the force of the pressure on the 
liquid at different depths. At A the press¬ 
ure is the least, because there is less weight of fluid abo\c. 
At 13 and C the fluid is driven outwards by the weight of that 
portion above, and the force will be strongest at C. 

440. As the lateral pressure arises solely 
from the downward pressure, it is not affected 
by the width nor the length of the vessel in 
which it is contained, but merely by its depth; 
for, as every particle acts independently of the 
rest, it is only the column of particles above the orifice that can 
weigh upon and press out the water. 


What effect has 
the length and 
the width of a 
body of fluid 
upon its lateral 
pressure ? 


To what is the 441. The lateral pressure on one side of a 
lateral pressure cubical vessel will be equal only to half of the 
pressure downwards; for every particle at the 
bottom of a vessel is pressed upon by a column of the whole depth 
of the fluid, while the lateral pressure diminishes from the bottom 
upwards to the surface, where the particles have no pressure. 


442. The upward pressure of fluids, although 
apparently in opposition to the principles of 
gravity, is but a necessary consequence of the 
operation of that principle; or, in other words, the pressure 
upwards , as well as the pressure downwards , is caused by gravity. 


What causes the 
upward pressure 
of a fluid ? 


443. When water is poured into a vessel with a 
Fi^Q 5 * spout (like a tea-pot, for instance), the water rises in 
the spout to a level with that in the body of the ves¬ 
sel. The particles of water at the bottom of the vessel are 
pressed upon by the particles aboye them, and to tuis pressure 
Miey will yield, if there is any mode of making way for the 





118 


NATURAL PHILOSOPHY. 


particles above them. As they cannot descend 
through the bottom of the vessel, they will 
change their direction and rise in the spout. 

Fig. 65 represents a tea-pot, and the columns 
of balls represent the particles of water magni¬ 
fied. From an inspection of the figure, it appears that the par¬ 
ticle numbered 1, at the bottom, will be pressed laterally by the 
particle numbered 2, and by this pressure forced into the spout, 
where, meeting with the particle 3, it presses it upwards, ana 
this pressure will be continued from 3 to 4, from 4 to 5, and so 
on, till the water in the spout has risen to a level with that in 
the body of the vessel. If water be poured into the spout, the 
water will rise in the same manner in the body of the vessel, 

from which it appears that the forcepf pressure 
of^jluid^pres- depends entirely on the height, and not on the 
sure. length or breadth, of the column of fluid. [<See 

No. 434.] 

444. Any quantity of fluid, however small, 
Hydrostatic ma y ma( ^ e to balance any other quantity 
Paradox t however large. This is what is called the Hy¬ 
drostatic Paradox.* 

Explain 445. The principle of what is called the hydro- 
Fig. 66. static paradox is illustrated by the hydrostatic bellows 
represented in Fig. 66 A B is a long tube, one inch square 
C I) E F are the bellows, consisting of two boards, eight inches 
square, connected by broad pieces of leather, or india-rubber 
cloth in the manner of a pair of common bellows. One pound 


Fig. 55. 



* A paradox is something which is seemingly absurd, but true in fact. But 
in what is called the Hydrostatic Paradox there is in reality no paradox at 
all. It is true that a small quantity of fluid will balance any quantity, 
however large, but it is on the same principle as that with which the longer 
arm of the lever acts. In order to raise the larger quantity of fluid, the 
smaller quantity must be elevated to a height in proportion as the bulk of 
the larger quantity exceeds the smaller. Thus, to raise 500 lbs of wate* 
by the descending force of one pound, the latter must descend 500 inches 
while the former is rising one inch ; and hence, what is called the hydro¬ 
static paradox is in strict conformity with the fundamental principle of Me¬ 
chanics, that what is gained in power is lost in time, or in space 




HYDK0STATIC8. 


119 


Fig. 



of water pourod into the tube will raise sixty- 
four pounds on the bellows. If a smaller 
tube be used, the same quantity of water will 
fill it higher, and, consequently, will raise a 
greater weight; but, if a larger tube be used, 
it will, of course, not fill it so high, and, con¬ 
sequently, will not raise so great a weight, 
because it is the height, not the quantity , which 
causes the pressure. 

The hydrostatic bellows may be constructed 
in a variety of forms, the simplest of which 
consists, as in the figure, of two boards connected together by 
broad pieces of leather, or india-rubber cloth, in such a manner 
as to allow the upper board to rise and fall like the common 
bellows. A perpendicular tube is so adjusted to this apparatus 
that water poured into the tube, passing between the boards, 
will separate them by its upward pressure, even although the 
upper board is loaded wiih a considerable weight. 

[N. B. A small quantity of water must be poured into the bellows fc< 
separate the surfaces before they are loaded with the weight.] 


How is the 
force of pres¬ 
sure cn the 
hydrostatic 
bellows esti¬ 
mated ? 


446. The force of pressure exerted on tko bel 
lows by the water poured into the tube is esti¬ 
mated by the comparative size of the tubo and 
the bellows. Thus, if the tube be one iuch square, 
and the top of the bellows twelve inches, thus 
containing 144 square inches, a pound of water poured into the 
tube will exert a pressure of 144 pounds on the b.;ilows. Now 
it will be clearly perceived that this pressure is caused by the 
height of the column of water in the tube. A pound, or a pint, 
of water will fill the tube 144 times as high as the same quantity 
would fill the bellows. To raise a weight of 144 pounds on the 
bellows to the height of one inch, it will be necessary to pour 
into the tube as nuich water as would fill the tube were it 144 
Wkcrt fund a- i nc ^ ies l° n g* It will thus be perceived that the 
mental law of fundamental principle of the hws of motion is 







120 


NATURAL PHILOSOPHY. 


, . here also in full force , namely , that iv ? uit is 

Mechanics ap • . J \ . 

p/ie$ fl /50 gained in power is lost either m time or in 

hydrostatic space; for, while the water in the bellows is 

prcssui e rising to the height of one inch, that in the tube 

passes over 144 inches. 

Explain 447. Another form of apparatus, by means of 

lig. 67. which it can be proved that fluids press in proportion 

to their perpendicular height, and not their quantity, is seen in 

Fig. 67. This apparatus unites simplicity with convenience. 

Instead of two boards, connected with leather, an india-rubber 

bag is placed between two boards, connected by crossed bars 

with a board below, loaded with weights, and the upper boards 

are made to rise or fall as the water runs into or out of the 

bag. It is an apparatus easily repaired, and the bag may also 

be used for gas, or for experiments in Pneumatics 

A and B are two vessels of unequal size, but of the same 

length. These may sue- 

6 . 1 , . Fig. 67. 

cessively be screwed to 

the apparatus, and filled 
with water. Weights 
may then be added to 
the suspended scale until 
the pressure is counter¬ 
balanced. It will then 
be perceived that, al¬ 
though A is ten times 
larger than B, the water 
will stand at the same 
height in both, because 
they are of the same 
length. If C be used 
instead of A or B, the 

apparatus may be used as the hydrostatic bellows/* 



* If a cask be filled with water, and a long pipe be fitted to it, by pouring 
water into the pipe it will exert so great a pressure as to burst the cask. 

In the same manner a mountain would bo rent asunder by hydrostatic 
picture, if a deep crevice, communicating with a gmall luuutain below, i a 
filled with water by the mi it 



















HYDROSTATICS. 


121 


448. Hydrosiatic Pressure used as a 
Mechanical Power. — If water be confined 
in any vessel, and a pressure to any amount 
be exerted on a square inch of that water, a 
pressure to an equal amount will be trans¬ 
mitted to every square inch of the surface of 
the vessel in which the water is confined. 

449. This property of fluids seems to invest us with a power of 
increasing the intensity of a pressure exerted by a comparatively 
small force, without any other limit than that of the strength of 
the materials of which the engine itself is constructed. It also 
enables us with great facility to transmit the motion and force of 
one machine to another, in cases where local circumstances pre¬ 
clude the possibility of instituting any ordinary mechanical con¬ 
nexion between the two machines. Thus, merely by means o* 
water-pipes, the force of a machine may be transmitted to any dis¬ 
tance, and over inequalities of ground, or through any other ob¬ 
structions. 


In wha* man¬ 
ner mat/ hy¬ 
drostatic pres¬ 
sure he em¬ 
ployed as a 
Mechanical 
Power ? 


On what prin¬ 
ciple is Bra- 
mali s hydro¬ 
static press 
constructed ? 
Explain Fig. 
68 . 


the cylinders, 
piston 8 carries a 
strong head P, which 
works in a frame op¬ 
posite to a similar 
plate It. Between 
the two plates tne 
Bubstance W to be 
compressed is placed. 
In the narrow tube, 
2 is a piston p, 
worked by a lever 
hd , its short arm 
11 


450. It is on the principle of hydrostatic press¬ 
ure that Bramah’s hydrostatic press, represented 
in Fig. 68, is constructed. The main features of 
this apparatus are as follows : a is a narrow, and 
A a large metallic cylinder, having communi¬ 
cation one with the other. Water stands in both 
The 

Fig. 68. 
































122 


NATURAL rillLOSOPHY. 


*lb driving the piston, while the power is applied at d. The 
pressure exerted by the small piston p on the water at a is 
transmitted with equal force throughout the entire mass of the 
fluid, while the surface ax A presses up the piston S with a 
force proportioned to its area. For instance, if the cylinder tz, 
of the force-pump has an area of half an inch, while the great 
cylinder has an area of 200 inches, then the pressure of the 
water in the latter on the piston S will be equal to 400 times 
that on p. 

Next, suppose the arms of the lever to be to each other as 
1 to 50, and that at d , the extremity of the longer arm, a man 
works with a force of 50 pounds, the piston p will consequently 
descend on the water with a force of 2500 pounds. Deducting 
one-fourth for the loss of power caused by the different impedi¬ 
ments to motion, and one man would still be able to exert a 
force of three-quarters of a million of pounds by means of this 
machine. This press is used in pressing paper, cloth, hay, gun¬ 
powder, &c.; also in uprooting trees, testing the strength of 
'topes, &c. 

When will one 

fluid float on 451. A fluid specifically lighter than another 

the surface of fluid w ifl fl oa t U p 0n its surface.* 
another fluid l 

[N. B. This is but another way of stating the law mentioned Id Nos. 409 
and 410.] 

452. If an open bottle, filled with any fluid specifically lighter 
than water, be sunk in water, the lighter fluid will rise from the 
oottle, and its place will be supplied with the heavier water. 

When will a ^53 • An y su ^ stance whose specific gravity is 

body rise , sink greater than any fluid will sink to the bottom of 
m a that fluid, and a body of the same specific gravity 
with a fluid will neither rise nor fall in the fluid 
but will remain in whatever portion of the fluid it is placed 


* The slaves in the West Indies, it is said, steal rum by inserting the 
long neok of a bottle, full of water, through the top aperture of the rum 
Ortsk. The water falls out of the bottle into the cask, while the lights 
cum asoeuds in its stead. 


HYIjKOSTATICS. 


123 


x>it a body whose specific gravity is less than that of a fluid 
will float. 

This is the reason why some bodies will sink and others float, 
and still others neither sink nor float.* 


How deep will 454. A body specifically lighter than a fluid 

a body sink in will sink in the fluid until it has displaced a por- 
a fluid! tion of the fluid equal in weight to itself. 

455. If a piece of cork is placed in a vessel of water, about one- 
third part of the cork will sink below, and the remainder will stand 
above, the surface of the water; thereby displacing a portion of 
water equal in bulk to about a third part of the cork, and this 
quantity of water is equal in weight to the whole of the cork 
because the specific gravity of water is about three times as great 
as that of cork. 

45G. It is on the same principle that boats, ships, &c., although 
composed of materials heavier than waiter, are made to float. From 
their peculiar shape, they are made to rest lightly on the water. 
The extent of the surface presented to the water counterbalances 
the weight of the materials, and the vessel sinks to such a depth as 
will cause it to displace a portion of water equal in weight to the 
whole weight of the vessel. From a knowledge of the specific 
gravity of water, and the materials of which a vessel is composed, 
rules have been formed by which to estimate the tonnage of vessels; 
that is to say, the w r eight wdiich the vessel w r ill sustain without 
sinking. 


What is the 
standard for 
estimating the 
specific grav¬ 
ity of bodies 1 


/ Ahl. The standard which has been adopted to 
estimate the specific gravity of bodies is rain or 
distilled water, at tho temperature of G0°.t 


* The bodies of birds that frequent the water, or that live in the Avater, 
are generally much lighter than the fluid in Avhich they move. The 
feathers and down of water-fowl contribute much to their buoyancy, but 
iishes ha\^e the power of dilating and contracting their bodies by means of 
an internal air-vessel,.which they can contract or expand at pleasure. 

The reason that the bodies of persons who have been drowned first sink, 
and, after a number of days, will float, is, that when first drowned the air 
being expelled from the lungs, makes the body specifically heavier than 
water, and it will of course sink ; but, after decomposition has taken place, 
the gases generated within the body distend it, and render it lighter than 
water, and they will cause it to rise to the surface. 

f As heat expands and cold condenses all metals, their specific gravity 
cannot be the same in summer that it is in winter. For this reason, they 
will not serve as a standard to estimate the specific gravity of other bodies 
The reason that distilled water is used is, that spring, wel’, or river water if 
6eidom perf( ctly pure, and the various substances mixed with it afl'ect it* 


124 


NATURAL PHILOSOPHY. 


This is found to be a very convenient standard, because a 
cubic foot of water at that temperature weighs exactly one 
thousand ounces. 

458. Taking a certain quantity of rain or distilled water, we find 
that a quantity of gold, equal in bulk , will weigh nearly twenty 
dimes as much as the water; of lead, nearly twelve times as much; 
while oil, spirit, cork, &c., will weigh less than water.* 


weight. The cause of the ascent of steam or vapor may be found in its 
specific gravity. It may here be stated that rain, snow and hail, are formed 
by the condensation of the particles of vapor in the upper regions of the 
atmosphere. Fine, watery particles, coming within the sphere of each 
Other’s attraction, unite in the form of a drop, which, being heavier than 
the air, falls to the earth. Snow and hail differ from rain only in the 
different degrees of temperature at which the particles unite. When rain, 
snow, or hail falls, part of it reascends in the form of vapor and forms 
clouds, part is absorbed by the roots of vegetables, and part descends into 
the earth and forms springs. The springs form brooks, rivulets, rivers, 
Ac., and descend to the ocean, where, being again heated by the sun, the 
water, rising in the form of vapor, agaiir forms clouds, and again descends 
in rain, snow, hail, Ac. The specific gravity of the watery particles which 
constitute vapor is less than that of the air near the surface of the earth ; 
they will, therefore, ascend until they reach a portion of the atmosphere of 
the same specific gravity with themselves. But the constant accession of 
fresti vapor from the earth, and the loss of heat, cause several particles to 
come within the sphere of each other’s attraction, as has been stated above, 
and they unite in the form of a drop, the specific gravity of which being 
greater than that of the atmosphere, it will fall in the form of rain. Water, 
as it descends in rain, snow or hail, is perfectly pure ; but, when it has 
fallen to the earth, it mixes with the various substances through which it 
passes, which gives it a species of flavor, without affecting its transparency. 

* TABLE OP SPECIFIC GRAVITIES. 


Temperature about 40° Fahrenheit. 


Distilled Water, 

1 . 

Palladium, 

11.500 

Mercury, 

13.596 

Iridium, 

18.650 

Sulphuric Acid, 

1.841 

Copper, 

8.850 

Nitric Acid, 

1.220 

Lead, 

11.250 

Prussic Acid, 

.696 

Bismuth, 

9.822 

Alcohol (pure), 

.792 

Tellurium, 

6.240 

Ether, 

.715 

Antimony, 

6.720 

Spirits of Turpentine 

.869 

Chromium, 

5.900 

Essence of Cinnamon, 

1.010 

Tungsten, 

17.500 

Sea Water, 

1.026 

Nickel, 

8.270 

Milk, 

1.030 

Cobalt, 

7.810 

Wine, 

.993 

Tin, 

7.293 

Olive Oil, 

.915 

Cadmium, 

8 687 

Naphtha, 

.847 

Zinc, 

7.190 

Iodine, 

4.946 

Steel, 

7.^20 

PUtinum, 

22.050 

Iron, 

7.788 

Gyii, 

19.360 

Cast-iron, 

7.200 

Silver, 

10.500 

Manganese, 

8.012 

Rhodium, 

11.000 

Sodium, 

971 




HYDROSTATICS. 


125 


tlou, is ihi. 


459. The specific gravity of bodies that will 
tfabody^s-^ s * n k water is ascertained by weighing them 
certained when first in water, and then out of the water, and 
dividing the weight out of the water by tb<j loss 
of weight in water. 


it is greater 
than that of 
water ? 


Potassium, 

.875 

Diamond, 

3.530 

Arsenic, 

5.670 

Graphite, 

2.500 

Phosphorus 

1.770 

Sulphur, 

2.086 

Lime, 

3.150 

Galena, 

7.580 

Marble, 

2.850 

White Lead, 

6.730 

Plaster of Paris, 

2.330 

Nitrate of Potash, 

1.930 

Emerald, 

2.700 

Garnet, 

3.350 

Feldspar, 

2.500 

Serpentine. 

2.470 

Alum, 

1.700 

Topaz, 

3.500 

Bituminous Coal, 

1.250 

Anthracite, 

1.800 

Pulverized Charcoal, 

1.500 

Woody Fibre, 

1.500 

Lignum Vitae, 

1.350 

Boxwood, 

1.820 

Beech, 

.852 

Ash, 

.845 


Elm, 

.800 

Yew, 

.807 

Apple Tree, 

.733 

Yellow Fir, 

.657 

Cedar, 

.561 

Sassafras, 

.482 

Poplar, 

.3h3 

Cork Tree, 

.240 

Flint Glass, 

3.330 

Pearls, 

2.750 

Coral, 

2.680 

China-ware, 

2.380 

Porcelain Clay, 

2.210 

Flint, 

2.600 

Granite, 

2.700 

Slate, 

2.825 

Alabaster, 

2.700 

Brass, 

8.300 

Ice, 

.865 

Common Air, 

.001 

Hydrogen Gas, 

.000105 

Living Men, 

.891 

Brandy, 

.820 

Mahogany, 

1.00? 

Chalk, 

1.793 

Carbonic Acid Gas, 

.001527 


By means of this table the weight of any mass of matter can be ascer 
tained, if we know its cubical contents. A cubic foot of water weighs 
exactly 1000 ounces. If we multiply this by the number annexed tc *ny 
substance in this table, the product will be the weight of a cubic foot of 
that substance. Thus anthracite coal has a specific gravity of 1.800. A 
thousand ounces, multiplied by this sum, produces 1800 ounces, which is 
the weight of a cubic foot of anthracite coal. 

The bulk of any given weight of a substance may also readily be ascer¬ 
tained by dividing that weight in ounces by the number of ounces there are 
in a cubic foot. The result will be the number of cubic feet. The cube 
root of the number of cubic feet will give the length, depth and breadth, of 
the inside of a square box that will contain it. 

It is to be understood that all substances whose specific gravity is greater 
than water will sink when immersed in it, and that all whose specific 
gravity is less than that of w r ater will float in it. Let us, then, tako a 
quantity of water which will weigh exactly one pound ; a quantity of the 
substances specified in the table, of the same bulk, will weigh as follows : 


Platinum, 
Fine Gold) 
Mercury, 
feud. 


22.050 lbs, 
19.300 “ 
13.596 “ 
11.250 «' 

11 * 


Silver, 

Copper, 

Iron, 

1 Glass, 


10.500 ios 
8.850 “ 
7.788 « 
3.330 « 




126 


NATURAL PHILOSOPHY. 


4G0. Fig. 69 represents 

Describe the, ... ... 

scales usd for taming the specific gravity 

fowling the of bodies. One scale is 

specific grav- s } 10rtcr t } ian the other, and 
lit/ oj a body. 

a hook is attached to the 
bottom of the scale, to which substances 
whose specific gravity is sought may be 
attached and sunk in water. 


the scales for ascer 

Fig. 69. 



461. Suppose a cubic inch of gold weighs nineteen ounces when 
weighed out of the water, and but eighteen ounces * when weighed 


Marble, 

2.850 lbs. 

Brandy, 

.820 lbs. 

Chalk, 

1.793 “ 

Living Men, 

.891 “ 

Coal. 

1.250 “ 

Ash, 

.845 “ 

Mahogany, 

1.003 “ 

Beech, 

.852 “ 

Milk, 

1.030 “ 

Elm, 

.800 “ 

Boxwood, 

1.320 « 

Fir, 

.07 « 

Rain Water, 

1.000 “ 

Cork, 

.240 “ 

Oil, 

.920 “ 

Common Air, 

.0011 « 

Ice, 

.865 “ 

Hydrogen Gas, 

.000105 “ 


A cubic foot of water weighs one thousand avoirdupois ounces. By mul¬ 
tiplying the number opposite to any substance in the above table by one 
thousand, we obtain the weight of a cubic foot of that substance in ounces. 
Thus, a cubic foot of platinum is 23,000 ounces in weight. 

In the above table it appears that the specific gravity of living men ia 
about one-ninth less than that of common water. So long, therefore, as 
the lungs can be kept free from water, a person, although unacquainted 
with the art of swimming, will not completely sink, provided the hands and 
arms be kept under water. 

The specific gravity of sea-water is greater than that of the water of 
fakes and rivers, on account of the salt contained in it. On this account, 
the water of lakes and rivers has less buoyancy, and it is more difficult to 
swim in it. 

* The gold will weigh less in the water than out of it, cn account of the 
upward pressure of the particles of water, which in some measure supports 
it, and, by so doing, diminishes its weight. Now, as the upward pressure 
of these particles is exactly sufficient to balance the downward pressure of 
a quantity of water of exactly the same dimensions with the gold, it follows 
that the gold will lose exactly as much of its weight in water as a quantity 
of water of the same dimensions with the gold will weigh. And this rule 
applies to all bodies, heavier than water, that are immersed in it. They 
will lost, as much oj their weight in water as a quantity of water of their own 
dimensions weighs. All bodies, therefore, of the same size, lose the same 
quantity of their weight in water. Jlence, the specific gravity of a body is the 
weight of it compared with that of water. As a body loses a quantity of its 
weight when immersed in water, it follows that when the body is lifted 
from the vater that portion of its weight which it had lost will be restored. 
This is the reason that a bucket of water, drawn from a well, is heavier 
when it rijes above the surface of the w T ater in the well than it is while it 
remains below the surface. Tor the same reason our limbs feel heavy in 
leaving a bith 









HYDROSTATICS. 


127 


m water, the lo3s in water is one ounce. The weight out of water 
nineteen ounces, being divided by one (the loss in Mater) , gives 
nineteen. The specific gravity of gold, then, would be nineteen ; 
or in other words, gold is nineteen times heavier than water. 

How is the spe- 462 ' The s P ecifio g raTit 3'.°f a body that will 
ific gravity of no ^ water is ascertained by dividing its 

t body lighter weight by the sum of its weight added to the 

ha 71 watcT • ° 

found? l° ss wei 'ght which it occasions in a heavy body 

previously balanced, in water.^ 


4G3. If a body lighter than water weighs six ounces, and, on being 
attached to a heavy body, balanced in water, is found to occasion it 
to lose twelve ounces of its weight, its specific gravity is determined 
by dividing its weight (six ounces) by the sum of its weight added 
to the loss of weight it occasions in the heavy body; namely, G 
added to 12, which, in other words, is 6 divided by 18, or 
which is 

464. Questions for Solution. 

(1.) A body lighter than water caused the loss of 10 lbs. to a heavier 
body immersed in water. In air the same body weighed 30 lbs. What 
wa3 its specific gravity 1 

Solution. — 30 lbs., its weight, divided by (30—10==) 40 (the sum of its 
weight added to the loss of weight which it caused in another body pre- 
v ously balanced in the water). .75. 

(2.) A body that weighed 15 lbs. in air weighed but 12 in water. What 
was its specific gravity 1 Ans. 5. 

(3.) If a cubic foot of water weigh 1000 ounces, what is the weight cf an 
e (ual bulk of gold 1 Am. 1210 lb. 

(4.) The weight of an equal bulk of lead 1 Ans. 703Z5. 2 oz. 

(o.) The weigut of an equal bulk of coHi 1 Ans. 15 lb. 


* The method of ascertaining the specific gravities of bodies was dis¬ 
et vered accidentally by Archimedes. He had been employed by the King 
of Syracuse to investigate the metals of a golden crown, which he suspected 
had been adulterated by the workmen. The philosopher labored at the 
problem in vain, till, going one day into the bath, he perceived that the 
water rose in the bath in proportion to the bulk of his body. He instantly 
perceived that any other substance of equal size would raise the water ji.st 
as much, though one of t^nnl weight and less bulk could not produce the 
same effect. He then obtained two masses, one of gold and one of silver, 
each equal in weight to the crown, and having filled a vessel very accu¬ 
rately'with water, he first plunged the silver mass into it, and observed the 
quantity of water that flowed over ; he then did the same with the gold, 
and found that a less quantity had passed over than before. Hence ho 
inferred that, though of e \ual weight, the bulk of the silver was greater 
than that of the gold, and that the quantity of water displaced was, in each 
experiment, equal to the bulk of the metal. He next made trial with the 
crown, and found that it displaced more water than the gold, and less than 
the silver, which led him to conclude that it was neither pure gold no t 
pure silver 


NATURAL PHILOSOPHY. 


128 


(6.) The weight of an equal bulk of iron 1 A <s. 486 7>. 12 •>* 

(7.) What is the weight of a cubic foot of mahogany 1 Ans. 62 lb. 11 oz. 
(8.) The weight of a cubic foot of marble 1 Ans. 178 lb. 2 oz. 

(9.) What is the weight of an iceberg 6 miles long, - mile wide, aud 
tOO feet thick 1 An *- 904,304.010 tons. 

(10.) What is the weight of a marble statue, supposing it to be exactly 
a yard and half of cubic measure 1 Ann. 7214,06 #>. + 

(11.) If a cubical body of cork exactly 9 inches on each side be placed 
in water, how deep will it sink 1 Ans - 2 - 16 in ; 

(12.) Suppose that 4 boats were made each out of one of the following 
kinds of wood, namely, ash, beech, elm and fir, which would carry the 
greatest weight without sinking 1 Ans. JhatoJJir. 


What is an 
Hydrometer ? 
arid on what 
principle is it 
constructed ? 


465. An Hydrometer is an instrument to 
ascertain the specific gravity of liquids. 

463. The hydrometer is constructed on the 
principle that the greater the weight of a 
liquid the greater will be its buoyancy. 


How is an hy- 467. The hydrometer is made in a variety of 
urometer con - forms, but it generally consists of a hollow ball 
structed? 0 f silver, glass, or other material, with a gradu¬ 
ated scale rising from the upper part. A weight is attached 
n^low the ball. When the instrument thus constructed is im¬ 
mersed in a fluid, the specific gravity of the fluid is estimated by 
the portion of the scale that remains above the surface of the 
fluid. The greater the specific gravity of the fluid, the less will 
the scale sink. 


Of what use 468. The hydrometer is a very useful instru- 
is the hydrom- ment for ascertaining the purity of many articles 
° ter ' in common use. It sinks to a certain determinate 

depth in various fluids, and if the fluids be adulterated the hy¬ 
drometer will expose the cheat. Thus, for instance, the specific 
gravity of sperm oil is less than that of whale oil, and Df course 
has less buoyancy. If, therefore the hydrometer does not sink 
to the proper mark of sperm oil, it will at once be seen that the 
article is not pure. 

Of what does 469. IIydraultcs. — Hydraulics treats of 
Hydraulics fluids in motion, and the instruments by which 
their motion is guided or controlled. 


HYDRAULICS. 


120 


470 This branch of Hydrodynamics describes thj effects of 
liquids issuing from pipes and tubes, orifices or apertuies, the 
motion of rivers and canals, and the forces developed in the 
action of fluids with solids. 


What quantity 
of a lii/uid will 
be dischargea 
from an orifice 
or pipe of a 
given size ? 


471. The quantity of a liquid discharged in a 
given time through a pipe or orifice is equal to a 
column of the liquid having for its base the orifice 
or the area of the bore of the pipe, and a height 
equal to the space through which the liquid would 
pass in the given time. 


472. Hence, when a fluid issues from an orifice in a vessel, it is 
.discharged with the greatest rapidity when the vessel from which it 
flows is kept constantly full.* This is a necessary consequence of 
the law that pressure is proportioned to the height of the column 
above. 


From what orifice 473. When a fluid spouts from several orifices 
will a fiuid spout in the side of a vessel, it is thrown with the 
to the greatest greatest random from the orifice nearest to the 
distance l centre. 


474. A vessel filled with any liquid will discharge a greater 
quantity of the liquid through an orifice to which a short pipe of 
peculiar shape is fitted, than through an orifice of the same size 
without a pipe. 

This is caused by the cross-currents made by the rushing of the 
water from different directions towards the sharp-edged orifice. 
The pipe smooths the passage of the liquid. But, if the pipe pro¬ 
ject into the vessel, the quantity discharged will be diminished, 
instead of increased, by the pipe. 

475. The quantity of a fluid discharged through a pipe or an 
orifice is increased by heating the liquid ; because heat diminishes 
the cohesion of the particles, which exists, to a certain degree, in 
all liquids. 


What part of 
a current of 
water flows 
most rapidly , 
and why ? 


476. Water, in its motion, is retarded by the 
friction of the bottom and sides of the channel 
through' which it passes. For this reason, the 
velocity of the surface of a running stream is 
always greater than that of any other part. 


* ’.» T ne velocity with which a liquid issues from an infinitely small orifice 
in ihe bottom or sides of a vessel that is kept full is equal to that which a 
neavy body would acquire by falling from the level of the surface to the 
level of the orifice. — 


180 


NATURAL PHILOSOPHY. 


477 In consequence of the friction of the banks and beds of 
rivers, and the numerous obstacles they meet in their circuitous 
course, their progress is slow. If it were not for these impediments, 
the velocity which the waters would acquire would produce very dis¬ 
astrous consequences.* An inclination of three inches in a mile, in 
the bed of a river, will give the current a velocity of about three 
miles an hour. 

478. To measure the velocity of a stream at its surface, hollow 
floating bodies are used ; as, for example, a glass bottle tilled with 
a sufficient quantity of water to make it sink just below the level of 
the current, and having a small flag projecting from the cork. A 
wheel may also be caused to revolve by the current striking against 
boards projecting from the circumference of the wheel, and the 
rapidity of the current may be estimated by the number of the rev¬ 
olutions in a given time. 


How may the 
velocity of a 
current at any 


479. The velocity of a current of water at any 
portion of its depth may be F . g 7Q 


depth be ascer- ascertained by immersing in 
tained ? it a bent tube, shaped like a 

tunnel at the end which is immersed. 

480. Fig. 70 is a tube shaped like a 
tunnel, with the larger end immersed in an 
opposite direction to the current. The 
rapidity of the current is estimated by the _ J _ 


height to which the water is forced into the 

tube, above the surface of the current. By 

Buch an instrument the comparative velocity 

of different streams, or the same stream at different times, may 

be estimated. 


How are waves 
caused f 


481. Waves are caused, first, by the friction 
between air and water, and secondly, and on a 
much grander scale, by the attraction of the sun and moon 
exerted on the surface of the ocean, producing the phenomena 
of the tides. 

482. The contriving hand of a benevolent Creator is seen more 
elearlv in nothing, than in the law's and operations of the mate¬ 
rial world. Were it not for the almost ceaseless motion of the water 
the ocean itself would become a putrid mass. Decayed and decaj,- 


see what is stated with regard to friction in Nos. ii73 anil 374 










HYDRAULICS. 


Id i 


n.g .flatter would be constantly emitting pestilential vapors, puison- 
ing the atmosphere, and spreading contagion and death to every 
breathing inhabitant of the earth. The “ ceaseless motion” mixes 
up the poisoncus ingredients, and prevents their floating on the 
surface.* 

483. The equilibrium of a fluid, according to recent discoveries, 
cannot be disturbed by waves to a greater depth than about three 
hundred and fifty times the altitude of the wave. 

484. When oil is poured on the windward side of a pond, th6 
whole surface will become smooth. The oil protects the water from 
the friction of the wind or air. It is said that boats have been pre¬ 
served in a raging surf, in consequence of the sailors having emptied 
a barrel of oil on the water. 


What are the 
principal hy¬ 
draulic instru¬ 
ments or ma¬ 
rlines 1 


485. The instruments or machines for 
raising or drawing water are the common 
pump, the forcing-pump, the chain-pump, the 
siphon, the hydraulic ram, and the screw of 
Archimedes. 


[The common pump and the forcing-pump will be 
noticed in connexion with Pneumatics, as their opera¬ 
tion is dependent upon principles explained in that 
department of Philosophy. The fire-engine is nothing 
more than a double forcing-jjjjjnp, and will be noticed in 
tne same connexion.] 



486. The Chain-pump is 

What is the a machine by which the water 
■ y/iain-purnp f J 

is lifted through a box or 
channel, by boards fitted to the channel 
and attached to a chain. It has been used 
principally on board of ships. 

487. Fig. 71 represents a Chain- 
Erplatn^ p um p. It consists of a square box 
through which a number of square 
ooards or buckets, connected by a chain, is 
tr‘*ie to pass. The chain passes over the wheel 
C and under the wheel D, which is under 
water. The buckets are made to fit the box, 


Fig. 71. 



* The undulations of large bodies of water have also produced material 
changes on the face of the globe, purposely designed by Creative Wisdom 
working by secondary causes, the uses of which are described in the scivnoe 
of Geology 



















132 


jSATUXAL PHILOSOPHY. 


>o as to move with little friction. The upper wheel C is turned 
by a crank (not represented in the Fig.',, which causes the chain 
with the buckets attached to pass through the box. Each 
bucket, as it enters the box, lifts up the water above it, and 
discharges it at the top. 



488. The screw of Archimedes is a ma- 

J Y hat ls the chine said to have been invented by the plfl- 
crew of Ar- > J 1 

chhnedes ? losopher Archimedes, for raising water and 
draining the lands of Egypt, about two hun¬ 
dred years before the Christian era. 

Fig. 72 repre- Fig. 72 

sents the screw of 
** Archimedes. A 
single tube, or two tubes, 
are wound in the form of 
a screw around a shaft or 
cylinder, supported by the 
prop and the pivot A, and 
turned by the handle n. 

As the end of the tube dips into the water, it is filled with the 
fluid, which is forced up the tube by every successive revolution, 
until it is discharged at the upper end. 

489. The Siphon is a tube bent in the form 
What is the of the letter U, one side being a little longer 

than the other, to contain a longer column 
of the fluid. 

490. Fig. 73 represents a Siphon. A Fi &- 73 * 
p-g yg siphon is used by filling it with water or /^\\ 
some other fluid, then stopping both ends, 
and m this state immersing the shorter leg or side 
into a vessel containing a liquid. The ends being then 
unstopped, the liquid will run through the siphon 
until the vessel is emptied. In performing this experi¬ 
ment, the end of the siphon which is out of the water 
*n«M always be below the surface of the water 


vnon * 


Erplo 










HYDRAULICS. 


136 


On n'h'U prin¬ 
ciple does the 
siphon act 1 


491 The principle on which the siphon acts 
is, that the longer column having the greater 
hydrostatic pressure, the fluid will run down in 
the diicction of that column. The upward pressure in the 
smaller column will supply a continued stream so long as that 
column rests below the surface of the water. 


[N. B. This principle will be better understood after the principle is ex¬ 
plained on which the operation of the common pump depends ; for the 
upward and downward pressure both depend on the pressure of the atmos 
phere.] 

492. The siphon may be used in exemplifying the equilibrium ot 
fluids ; for, if the tube be inverted and two liquids of different 
density poured into the legs, they will stand at a height in an in¬ 
verse proportion to their specific gravity. Thus, as the specific 
gravity of mercury is thirteen times greater s than that of water, a 
column of mercury in one leg will balance a column of water in the 
other thirteen times higher than itself. But, if but one fluid be 
poured into both legs, that fluid will stand at equal height in both 

Explain the toy 493. ^be ca ^ e ^ Tantalus’ * Cup consists 
called Tantalus ’ of a goblet containing a wooden figure, with a 
^ U P • siphon concealed within. The water being 

poured into the cup until it is above the bend of the siphon, 
rises in the shorter leg, which opens into the cup, and runs out 
at the longer end, which pierces the bottom. 

Fig. 74. 

494. Fig. 74 represents the cup with the siphon, 
the figure of the man being omitted, in order that the 
position of the siphon may be seen. 

495. The Hydraulic Ram f is an inge- 
^trauiic Ram l~ n i° u s machine, constructed. for the purpose 
of raising w r ater by means of its own im- 
* pulse or momentum. 



* Tantalus, in Heathen mythology, is represented as the victim of per¬ 
petual thirst, although placed up to the chin in a pool of water ; for, as soon 
as he attempts to stoop to drink, the water flows away from bis grasp ; 
hence our English word tantalize takes its origin. In the toy described 
above, the siphon carries the water away before it reaches the mouth of the 


figure. 

t Iho Hydraulic Ram, sometimes called by its French name, Et*.- 
12 


Hv 




134 


NATURAL PHILOSOPHY. 


496 lu tlie construction of an hydraulic ram, there must ca, 
in the first place, a spring or reservoir elevated at least four oi 
five feet above the horizontal level of the machine.^ 

Secondly , a pipe must conduct the water from the reservoir 
to the machine with a descent at least as great as one inch for 
every six feet of its length. 

Thirdly a channel must be provided by which the superflu¬ 
ous water may run off. 


497. The ram itself consists of a pipe having two apertures, 
both guarded by valves of sufficient gravity to fall by their own 
weight, one of which opens downwards, the other opening up¬ 
wards into an air-tight chamber. An air-vessel is generally 
attached to the chamber, for the purpose of causing a steady 
stream to flow from the chamber, through another pipe, to the 
desired point where the water is to be discharged. 

Explain the con- 498 - Fi S- 75 represents the hydraulic ram. 
struction of the A B represents the tube, or body of the ram, 
Hydraulic* Ram having two apertures, C andD, both guarded by 
valves; C opening downwards,. D opening up- 


drauliqve , in its present form, was. invented by Montgolfier, of Montpelier 
An instrument or machine of a similar construction had been previously 
constructed by Mr. Whitehurst, at Chester, but much less perfect in its 
mode of action, as it required to be opened and shut by the hand by 
means of a stop-cock. Montgolfier’s machine, on the contrary, is set, in 
motion by the action of the water itself. 

* Such an elevation may easily be obtained in any brook or stream of 
running water by a dam at the upper part of the stream, to form a reser¬ 
voir. It has been calculated that for every foot of fall in the pipe running 
from the reservoir to the ram sufficient power will be obtained t$ raise 
about a sixth part of the water to the height of ten feet. With a fall of only 
four feet and a half, sixty-three hundred gallons of water have been raised 
tq the height of one hundred and thirty-four feet. But, the higher the res¬ 
ervoir, the greater the force with which the hydraulic ram will act. The ope 
ration of the principle by which the hydraulic ram acts is familiar to those 
who obtain water for domestic purposes by means of pipes from an elevated 
reservoir, as is the case in many of our large cities. A sudden stoppage of 
the flow, by turning the cock too quickly, causes a jarring of the pipes, which 
is distinctly perceived, and often loudly heard all over the building. This 
is due to the sudden change from a state of rapid motion to a state of rest. 
The ineitia of the fluid, or its resistance to a change from a state of rapid tuo. 
tion to a state of rest, a property which it possesses in common with all other 
Rinds of matter, explains the cause of the violent jarring of the pipes, the 
stopping of which arrests the motion of the fluid ; and the violence, which 
ib in exact proportion to the momentum of the fluid, is sometimes so great 
it t (/ burst the pipes 


HYDRAULICS. 


I‘55 

wards, and both falling by their own weight. .Let us now suppose 
the valve C to be open and D shut. The water, descending through 
the tube A. B with a force proportionate to the height of the 

Pig. 76. 



reservoir, forces up the valve C and closes the aperture, thus 
suddenly arresting the current, and causing, by its reaction, a 
pressure throughout the whole length of the pipe ; this pressure 
forces up the valve D, and causes a portion of the water to enter 
the chamber above D. The current having thus spent its force, 
the valve C immediately falls by its own weight, by which 
means the current is again permitted to flow towards the aper¬ 
ture C. The pressure at D thereby being removed, that valve 
immediately falls, and closes the aperture. When this takes 
place, everything is in the same state in which it was at first. 
The water again begins to flow through the aperture at C, again 
closing that valve, and again opening D ; and the same effects are 
repeated at intervals of time, which, for the same ram, undergo 
but little variation. 

The water being thus forced into the chamber E, as it cannot 
return through the valve D, it must proceed upwards through 
the pipe G, and is thus carried to any desired point of dis¬ 
charge. An air-vessel is frequently attache 4 to the chamber 





















136 


NATURAL PHILOSOPHY. 


of tho ram, which performs the same office as it does m the 
forcing-pump, namely, to cause a steady stream to flow from 
the pipe G. The action, both of the ram and the forcing-pump, 
without the air-vessel, would be spasmodic.* 

How are Springs 499 - Sl>KINGa aND Spring, an3 

and Rivulets Rivulets are formed by the water from rain, 
formed ? snow, &c., which penetrates the earth, and 

descends until it meets a substance which it cannot penetrate. 
A reservoir is then formed by the union of small streams under 
ground, and the water continues to accumulate until it finds an 
outlet. 

Fig. 76. 


7/i 



Fig. 76 represents a vertical section of the crust of the eartl 
a, c, and e are strata, either porous, or full of cracks, which per 
mit the water to flow through, while b y d and f, are impervious 
to the water. Now, according to the laws of hydrostatics, the 
water at b will descend and form a natural spring at g: at i it 
will run with considerable force, forming a natural jet; and at 
l , p and g, artesian wells may be dug, in which the water will 
rise to the respective heights g k, p 1c , and l m, the water not 

* The simplicity and economy of this mode of raising water have caused 
it to be quite extensively adopted in the Northern States. When well con¬ 
structed, an hydraulic ram will last for years, involving no additional 
trouble and expense, more than occasionally leathering the valves when 
they have been too much worn by friction. The origin of the name will be 
readily perceived from the mode of its action. 

“ Et potum pastas age, Tityre et inter agendum, 

Occursare capro, cornu font ille> caveto ”— Virg. Bucolic 9, v. 25 












faYDKATTLICS. 


13? 


being allowed to come in contact with the porous soil through 
which the bore is made, but being brought in pipes to the sur¬ 
face ; at n the water will ascend to about o. and there will be 
no fountain. This explains, also the manner in which water i 
obtained by digging wells. 

How high wiii 500 * A s P rin s wil1 rise nearl y as hi S h > but 
the water of a cannot rise higher than the reservoir from 
spring rise ? whence it issues. 

Friction prevents the water from rising quite as high as the reser¬ 
voir. 

To what height 501. Water may be conveyed over hills and val- 
may water be leys in bent pipes and tubes, or through natural 
conveyed in passages, to any height which is not greater than 
tubes ? the level of the reservoir from whence it flows. 


502. The ancient Romans, ignorant of this property of fluids, 
constructed vast aqueducts across valleys, at great expense, to con¬ 
vey water over them. The moderns effect the same object by means 
of wooden, metallic, or stone pipes. 


How are foun¬ 
tains formed? 


Explain the 
fountain by 
Fig. 76. 


503. Fountains are formed by water carried 
through natural or artificial ducts from a reser¬ 
voir. The water will spout from the ducts to 
nearly the height of the surface of the reservoir. 

504. In Fig. 76 a fountain is represented at i, 
issuing from the reservoir, the height of which is 
represented by a c. The jet at i will rise nearly 
as high as c. 

505. A simple method of making an artificial 
fountain may be understood by Fig. 77. A 
glass siphon ah c is immersed in a vessel of 
water, and the air being exhausted from the 
siphon, a jet will be produced at a, proportioned 
to the fineness of the bore and the length of the 
tube. 


/ig. 77. 


ft' 


[N. B. The force of this kind of artificial jet is in 
a great measure dependent on a pneumatic priuciplo.] 

12 * 



u 









138 


NATURAL PHILOSOPHY. 


506. Hero’s Fountain. — The hydraulic instrument called 
Hero’s Fountain is an apparatus for projecting water by means 
of the pressure of confined air. 

Fig. 78 represents Hero’s Fountain. It consists of two ves¬ 
sels, both air-tight, and communicating by a 
pipe, which, being inserted into the top of the 
lower vessel, reaches nearly to the top of the 
upper vessel, which is in two parts, the upper 
part being filled with water, which descends in 
a pipe seen on the right in the figure to the 
lower vessel, and, as it fills the lower vessel 
condenses the air, forcing it up through the left- 
hand pipe, and causing it to press on the sur¬ 
face of the water in the lower part of the upper 
vessel. The water in the upper vessel is thus 
forced through the central pipe in a jet, to a 
height nearly as great as the length of the pipe on the right. 
The supply of water is furnished in the upper part of the upper 
vessel, which may always be kept full by any external supply. 

507. Mechanical Agency of Fluids.— 

How does water , T7 - , , i t L o 

become a me- Water becomes a mechanical agent ot great 

chemical agent? power by means of its weight, its momentum 

and its fluidity. 

Tt is used as the moving power of presses, to raise portions of 
itself, and to propel or turn wheels of different constructions, 
which, being connected with machinery of various kinds, form 
mills and other engines, capable of exerting great force. 

What is Pneu- 508. Pneumatics. — Pneumatics treats of 
mattes? the mechanical properties and effects of air 

and similar fluids, called elastic fluids and gases, or aeriform 
fluids. 



What is meant 
by an af'iform 
fluid ? 


509. Aeriform fluids are those which have the 
form of air Many of them are invisible,^ or 


* Gases ait invisible, except when colored, which happens <»n ly in a 
few instances 










PNEUMATICS. 


i:jy 


nearly so, and all of them perform very important operations in 
the mateiial world. But, notwithstanding that they are in 
most instances imperceptible to our sight, they are really 
material, and possess all the essential properties of matter. 
They possess, also, in an eminent degree, all the properties 
which have been ascribed to liquids in general, besides others 
by which th3y are distinguished from liquids. 

What is the 510. -^ as ^ c are divided into two classes, 
difference be- namely, permanent gases and vapors. The gases 
tween a perma- cannot be converted into the liquid state by any 
a 6 vapor f an known process of art ;*but the vapors are readily 

reduced to the liquid form either by pressure or 
diminution of temperature. There is, however, no essential dif¬ 
ference between the mechanical properties of both classes of fluids. 


What subjects 511. ^ ie a ^ r w ^ich we breathe, and which 
are embiaced surrounds us, is the most familiar of all this class 
in the science 0 f bodies, it is generally selected as the subject 
of Pneumatics* ^ p neuma ^ cs> ]3 u t ft must be premised that 

the same laws, properties and effects, which belong to air , belong 
in common, also, to all aeriform fluids or gaseous bodies. 


512. There are two principal properties of air, 
What are the namdy» gravity and elasticity. These are called 
wo principal the principal properties of this class of bodies, 
air^and^ther ^ ecause they are the means by which their pr es¬ 
teems bodies? ence and mechanical agency are especially ex¬ 
hibited. 

What degree 513. Although the agriform fluids all have 

of cohesive at- we ]oht, they appear to possess no cohesive at- 
tract ion hare J 11 

gaseous bodies? traction. 

514. The great degree of elasticity possessed by all aeriform 
fluids, renders there susceptible of compression and expansion to an 
almos- unlimited extent. The repulsion of their particles causes 
them to expand, while within certain limits they are easi'y cow- 


* Carconic acid gas forms an exception to this remark. Water also •» 
Jie 7 .♦no . of oxygon and hydrogen gas. 


140 


NATURAL PHILOSOPHY 


pressed. This materially affects the state of density ai ' ranty 
under which they are at times exhibited.* 


7 515. It may here be stated, that all t ie laws 

What laws ...... , . . . . . 

pertain to aeri- and properties ot liquids (which have been de- 

forrn bodies in scribed under the heads of Hydrostatics and 

general l Hydraulics) belong also to aeriform fluids. 

The chemical properties of both liquids and fluids belong pecu¬ 
liarly to the science of Chemistry, and are not, therefore, considered 
in this volume. 


What is the 
air which we 
breathe ? 


516. The air which we breathe is an elastic 
fluid, surrounding the earth, and extending 
to an indefinite distance above its surface, and 


constantly decreasing upwards in density. 


Where is the 
air in its most 
condensed 
form , and 
why ? 


517. It has already been stated th «i the air 
near the surface of the earth bears the weight of 
that which is above it. Being compressed, there¬ 
fore, by the weight of that above it, it must exist 
in a condensed form near the surface of the 
earth, while in the upper regions of the atmosphere, where 
there is no pressure, it is highly rarefied. This condensation, 
or pressure, is very similar to that of water at great depths in 
the sea.t 


518. As the air diminishes in density upwards, it follows 
that it must be more rare upon a hill than on a plain. In very 
elevated situations it is so rare that it is scarcely fit for respir¬ 
ation or breathing, and the expansion which takes place in the 
more dense air contained within the body is often painful. It 


* The terms “ rarefaction ” and “ condensation and ** rarefied *’ and “ con 
densed must be clearly understood in this connexion. They are applied 
respectively to the expansion and compression of a body. 

t The air is necessary to animal and vegetable life, and to combustion. 
It is a very heterogeneous mixture, being filled with vapors of all kinds. 
It consists, however, of two principal ingredients, called oxygen and 


PNEUMATICS. 


m 


occasions distension, and sometimes causes the bursting, of the 
smaller blood-vessels in the nose and ears. Besides, in such 
situations we are more exposed both to heat and cold; for, 
though the atmosphere is itself transparent, its lower regions 
abound with vapors and exhalations from the earth, which float 
in it, and act in some degree as a covering, which preserves us 
equally from the intensity of the sun’s rays and from the 
severity of the cold. 

519. Besides the two principal properties, gravity * and elasticity, 
the operations of which produce most of the phenomena of Pneu¬ 
matics, it will be recollected that as air, although an invisible is 
yet a material substance, possessing all the common properties of 
matter, it possesses also the common property of impenetrability. 
This will be illustrated by experiments. 


520. The pressure of the atmosphere caused 
by its weight is exerted on all substances, inter¬ 
nally and externally, and it is a necessary conse¬ 
quence of its fluidity. The body of a man of 
common stature has a surface of about 2000 
square inches, whence the pressure, at 15 pounds 
per square inch, will be 30,000 pounds. The 
reason why this immense weight is not felt is, 
that the air within the body and its pores counterbalances the 
weight of the external air. When the external pressure is arti¬ 
ficially removed from any part, it is immediately felt by the 
reaction of the internal air. 


Where is the 
pressure of the 
air felt ? 

What pressure 
docs a man of 
common stat¬ 
ure experience 
from the 
weight of the 
air t 


521. Heat insinuates itself between the particles 
has heat upon of bodies and forces them asunder, m opposition 
air and other to the attraction of cohesion and of gravity ; it 
elastic fluids ? therefore exerts its power against both the attrac¬ 
tion of gravitation and the attraction of cohesion. But, as the 
attraction of cohesion does not exist in aeriform fluids, the 
expansive power of heat upon them has nothing to contend with 


* It has been computed that the weight of the whole atmosphere is equal 
to that of a globe of lead sixty miles in diameter, or to live thousand 
hiliious of tons. 


142 


NATURAL PHILOSOPHY. 


but gravity. Any increase of temperature, therefcre, expands 
an elastic fluid prodigiously, and a diminution of heat con¬ 
denses it. 

. , 522. A column of air, having a base an inch 

weight of a square, and reaching to the top or the atrno- 
co/umn of air sphere, weighs about fifteen pounds. This press- 

Tsquare mch? ure ’ like the P ressure of liquids, is exerted 
equally in all directions. 

What is meant 523. The elasticity of air and other aeriform 

by the elasticity fl u id s j s that property by which they are in- 
of air and . ....... , .. 

other aeriform creased or diminished in extension, according as 

fluids ? they are compressed. 


What effect 524. This property exists in a much greater 
has an increase degree in air and other similar fluids than in any 

or a di/ninu- 0 ^ cr substance. In fact, it has no known limit, 
tion of pressure # * 

upon an a'eri- for, when the pressure is removed from any por- 

form body ? tion of air, it immediately expands to such a 
degree that the smallest quantity will diffuse itself^over an 
indefinitely large space. And, on the contrary, when the press¬ 
ure is increased, it will be compressed into indefinitely smal. 
dimensions. 


What is Ma~ 525. The elasticity or pressure of air and 
riotte's Law ? a p g ages ] s j n direct proportion to their dens¬ 
ity ; or, what is the same thing,, inversely proportional to 
the space which the fluid occupies. This law, which was 
discovered by Mariotfp, is called “ Mariotte's Law 
This law may perhaps be better expressed in the following 
language; namely, the density of an elastic fluid is in 
direct 'proportion to the pressure which it sustains. 

How does air 526. Air becomes a mechanical agent by 
become a me- „ . ... . . ° . 

chanical means of its weight, its elasticity, its inertia 

agent ? and its fluidity. 


With what 527. The fluidity of ^ir invests ?r, as it invests 
vowei does all other liquids, with ihr power of transmitting 


PNEUMATICS. 


M3 


What is a 
Vacuum ? 


What is the 
most perfect 
vacuum that 
has been ob¬ 
tained? 


fhudity invest pressure. But it has already been- shown, under 
the head of Hydrostatics, that fluidity is a neces¬ 
sary consequence of the independent gravitation of the particles 
of a* •* fluid. It may, therefore, be included among the effects of 
weight. 

528. The inertia of air is exhibited in the resistance which it 
opposes to motion, which has already been noticed under the head 
ot Mechanics.* This is clearly seen in its effects upon falling 
bodies, as will be exemplified in the experiments with the air-pump. 

529. A Vacuum is a space from which air 
and every other substance have been removed 

530. The Torricellian vacuum was discovered 
by Torricelli, and was obtained in the following 
manner : A tube, closed at one end, and about 
thirty-two inches long, was filled with mercury ; 
the open end was then covered with the finger, so 

as to prevent the escape of the mercury, and the tube inverted 
and plunged into a vessel of mercury. The finger was then 
removed, and the mercury permitted to run out of the tube. It 
was found, however, that the mercury still remained in the tube 
to the height of about thirty inches, leaving a vacuum at the 
top of about two inches. This vacuum, called from the dis- 
ioverer the Torricellian vacuum, is the most perfect that has 
been discovered.! 


* The fly, as it is called, in the mechanism of a clock by which the hours 
are struck, is an instance of the application of the inertia of the air in 
Mechanics. 

f Torricelli was a pupil of the celebrated Galileo. The Grand Duke of 
Tuscany having had a deep well dug, the workmen found that the water 
would rise no higher than thirty-two feet. Galileo was applied to for an 
explanation of the reason without success. Torricelli conceived the idea of 
substituting mercury for water, arguing that if it was the pressure of the 
atmosphere that would raise the water in the pump to the height of thirty- 
two feet, that it would sustain a column of mercury only one-fourteenth as 
high, or thirty inches only, on account of its greater specific gravity. lie 
therefore determined to test it by experiment. He accordingly filled a 
small glass tube, about four feet long, with mercury, and, stopping the 
open end with his finger, he inverted it into a basin of mercury. On 
removing his finger, the mercury immediately descended in the tube, and 
stood at the height of about thirty inches ; thus demonstrating the fact 
that it was the pressure of the air on the surface of the mercury in the one 

•*aae, and of the water in the other, that sustained the column of mercury 
to the tube, and of the water in the pump, 




144 


NATURAL PHILOSOPHY. 


531. As this is one of the most important discoveries of the 
science of Pneumatics, it is thought to be deserving of a labored 
explanation. The whole phenomenon is the result of the equilibrium 
of fluids. The atmosphere, pressing by its weight (fifteen pounds 
on every square inch) on the surface of the mercury in the vessel, 
counterpoised the column of mercury in the tube w r hen it was about 
thirty inches high, sho\ving..thereby that a column of the atmo 
sphere is equal in weight to a column of mercury of the same base, 
having a height of thirty inches. Any increase or diminution in 
the density of the air produces a corresponding alteration in its 
weight, and, consequently, in its ability to sustain a longer or a 
shorter column of mercury. Ilad water been used instead of mer¬ 
cury, it would have required a height of about thirty-three feet to 
counterpoise the weight of the atmospheric column. Other fluids 
may be used, but the perpendicular height of the column of any 
fluid, to counterpoise the weight of the atmosphere, must be as 
much greater than that of mercury as the specific gravity of mercury 
exceeds that of the fluid employed. 

532. This discovery of Torricelli led to the construction of the 
Oarometer,* for it wais reasoned that if it was the weight of the 
atmosphere which sustained the column of mercury, that on ascend¬ 
ing any eminence the column of mercury would descend in pro¬ 
portion to the elevation. 

What is a Ba- 533. The Barometer is an instrument to 
romeier ? measure the weight of the atmosphere, and 
thereby to indicate the variations of the weather, f 

534. Fig. 83 represents a barometer. It 
Kxplain cons } s t s 0 f a } 01 g glass tube, about thirty- 
three inches in length, closed at the upper 
end and filled with mercury. The tube is then in- 
ver ed in a cup or leather bag of mercury, on which 
the pressure of the atmosphere is exerted. As the 
tube is closed at the top, it is evident that the mercury 
cannot descend in the tube without producing a vacuum. 

The pressure of the atmosphere (which is capable of 
supporting a column of mercury of about thirty inches 
in height) prevents the descent of the mercury ; and 

* Among those to whom the world is indebted for the invention of the 
barometer, and its applications in science, may be mentioned the names oi 
Descartes, Pascal, Morienne and Hoyle. The original idea is due to Terri 
celli’s experiment. 

t The word barometer is from the Greek, and siguifies “ a measure of tfm 
*>eiu>a ” that is, of the atmosphere. 


Fig. 79. 





PNEUMATICS. 


145 


Fig. 80. 


tho instrument, tnu* constructed, becomes an implement for 
ascertaining the weight of the atmosphere. As the air varies 
in weight or pressure, it must, of course, influence the mercury 
in the tube, which will rise or fall in exact proportion with the 
pressure. When the air is thin and light, the pressure is less, 
and the mercury will descend; and, when the air is dense and 
heavy the mercury will rise.* At the side of the tube there 
is a scale, marked inches and tenths of an inch, to note the rise 
and fall of the mercury. 

535. The barometer, as thus constructed, only required the 
addition of an index and a weather-glass, as seen 
in Fig. 80, tc give a fair and true announcement 
of the state and weight of the atmosphere. The 
instruments arc now manufactured in several dif¬ 
ferent forms. The different forms of the barometer 
in general use are the common Mercurial Barom¬ 
eter, the Diagonal, and the Wheel Barometer, all 
of which are constructed with a column of mer¬ 
cury. The Aneroid or Portable Barometer is a 
new instrument, in which confined air is substi¬ 
tuted for mercury. This is a convenient form of 
the instrument for portable purposes. But the 
principle is the same in all, and repeated observa¬ 
tions during the ascent of the loftiest mountains 
in Europe and America have confirmed the truth , 
of barometrical announcements; for, by its indi¬ 
cations, the respective heights of the acclivities in 
high regions can now be ascertained by means of 
this instrument better than by any ot'er course, 

— with this advantage, too, that no prop^ "tionate ** 
height need be known to ascertain the altitucu * 



m. 


77. 


w 


* Tho elasticity of the air causes an increase or diminution of its bulk, 
accoiding as it is affected by heat and cold ; and this increase and diminu 
tion of bulk materially affect its specific gravity. The height of a columr, 
of mercury that can be sustained by a column of the atmosphere must, 
therefore, be affected by the state of the atmosphere. 

t From the explanation which has n- * been given of the b vuieter, it 
18 


















146 


NATURAL PHILOSOPHY. 


.. , . 536. The pressure of the atmosphere oa tti* 

On what prin - 1 r 

dpleis the ba - mercury, in the bag or cup of a barometer, being 
rcmeter con- exerted on the principle of the equilibrium of 

fluids, must vary according to the situation it* 
which the barometer is placed. For this reason, it will be th» 
greatest in valleys and low situations, and least on the top of 
high mountains. Hence the barometer is often used to ascer 
tain the height of mountains and other places above the ’evel of 
the sea. 

When is the 537. The air is the heaviest in dry weather, 
atmosphere and consequently the mercury will then rise 
heaviest ? highest. In wet weather the dampness renders 

will readily be seen that a column of any other fluid will answer as well as 
mercury, provided the tube be extended in an inverse proportion to the 
specific gravity of the fluid. But mercury is the most convenient, because 
it requires the shortest tube. 

In navigation* the barometer has become an important element of 
guidance, and a most interesting incident is recounted by Captain Basil 
Hall, indicative of its value in the open sea. While cruising off the coast 
of South America, in the Medusa frigate, one day, when within the tropics, 
the commander of a brig in company was dining with him. After dinner 
the conversation turned on the natural phenomena of the region, when 
Captain Hali's attention was accidentally directed to the barometer in the 
state-room where they were seated, and, to his surprise, he observed it to 
evince violent and frequent alteration. His experience told him to expect 
bad weather, and he mentioned it to his friend. 11»3 companion, however, 
only laughed, for the day was splendid in the extreme, the sun was shining 
with its utmost brilliance, and not a cloud specked the deep-blue sky 
above. But Captain Hall was too uneasy to be satisfied with bare appear¬ 
ances. He hurried his friend to his skip, and gave immediate directions 
for shortening the top hamper of the frigate as speedily as possible. Ilia 
lieutenants and the men looked at him in mute surprise, and one or two of 
the former ventured to suggest the inutility of the proceeding. The cap¬ 
tain, however, persevered. The sails were furled, the top-masts were 
struck ; in short, everything that could oppose the wind was made as 
snug as possible. His friend, on the contrary, stood in under every sail. 

The wisdom of Captain Hall’s proceedings was, however, speedily evi¬ 
dent ; just, indeed, as he was beginning to doubt the accuracy of his 
instrument. For hardly f *d the necessary preparations been made, and 
while his eye was rant* jg over the vessel to see if his instructions had 
been obeyed, a dark ^azy hue was seen to rise in the horizon, a leaden 
tint rapidly overspread the sullen waves, and one of the most tremendous 
hurricanes burst upon the vessels that ever seaman e".countered on his 
ocean home. Tne sails of the brig were immediately torn to ribbons, her 
masts went by the board, and she was left a complete wreck on the tem¬ 
pestuous surf which iaged around her, while the frigate wap dri.v?n wildly 
along at a furious rate, and had to scud under bare poles 'icv< ss tne wide 
Pacific, full three thousand miles, before it could be said t/.i.t bi.u was iv 
tuk-ky Trow the blast 


PNEUMATICS. 


14V 


•* e air less salubrious, and it appears, therefore, :nore heavj 
then, ah hough it is, in fact, much lighter. 


538. The greatest depression of the barometer 
occurs daily at about four o’clock, both in the morn¬ 
ing and in the afternoon; and its highest elevation 
at about ten o'clock, morning and night. In sum 
mer these extreme points are reached an hour or 
two earlier in the morning, and as much later in the afternoon. 


A. what time 
oj the day is 
the highest 
and lowest 
state of the 
barometer ? 


539. Rules have been proposed by which the changes of the 
weather may be predicted by means of the barometer, hence 
the graduated edge of the instrument is marked with the words 
“ rain," “fair," “ changeable .” “frost," &c. These expressions 
are predicated on the assumption that the changes of the weather 
may correctly be predicted by the absolute height of the mercury. 
But on this little reliance can be placed. The best authorities agree 
that it is rather the change in the height on which the predications 
must be made. 

540. As the barometer is much used at the present day, it has 
been thought expedient to subjoin a few general and special rules, 
from different authorities, by which some knowledge of the uses of 
the instrument may be acquired. 

541. General Rules by which Changes of the Weather may be prognost j 

cated by means of the Barometer.* ^ 

(1.) Generally the rising of the mercury indicates the approach of fair 
weather. 

(*2.) In sultry weather the fall of the mercury indicates coming thunder 
In winter the rise of the mercury indicates frost In frost, its fall indicates 
thaw, and its rise indicates snow. 

(:{.) Whatever change of weather suddenly follows a shango in the 
barometer, may be expected to last but a short time. Thus, if fair weather 
follow immediately the rise of the mercury, there will be very little of it, 
and, in the same way, if foul weather follow the fall of the mercury, it will 
last but a short time. 

M.) If fair weather continue for several days,during which the mercury 
continually falls, a long succession of foul weather will probably ensue; and 
again, if foul weather continue for several days, while the mercury con¬ 
tinually rises, a long succession of fair weather will probably succeed. 

(5.) A fluctuating and unsettled state in the mercurial column indicates 
changeable weather. — Lurdner,page 75, Pneumatics. 


54*i Special Rules byjvhich we may know the Changes of the Weather by 
means of the Barometer .f 

The barometer is highestof ail during a long frost, and it generally 
rises with a north-west wind. 


* These rules, says Dr. Lardner, fron whose work they are extr..cteu 
may to some extent be relied upon, but they are subject to some u-ioei 
tainty. 

f These rules art from a different authority. 


L48 


NATURAL PHILOSOPHY. 


(2 ) The barometer is lowest of all during a thaw which f olIows a long 
frost, and it generally falls with a south or east wind. 

(3.) While the mercury in the barometer stands above 30° the air must 
ae very dry or very cold, or perhaps both, and no rain may be >xpected. 

(4.) W hen the mercury stands very low indeed, there will never be much 
rain, although a fine day will seldom occur at such times. 

(3.) In summer, after a long continuance of fair weather, the barometer 
A-ill fall gradually for two or three days before rain falls ; but, if the fall 
jf the mercury be very sudden, a thunder-storm may be expected. 

(ti.) When the sky is cloudless and seems to promise fair weather, if the 
•barometer is low, the face of the sky will soon be suddenly overcast. 

(7.) Dark, dense clouds will pass over without rain when the barometer 
is high ; but if the barometer be low it will often rain without any appear¬ 
ance of clouds. 

(8.) The higher the mercury, the greater probability of fair weather. 

(y.) When tho mercury is in a rising state, fine weather is at naud ; but 
when the mercury is in a falling state, foul weather is near. 

(10.) In frosty weather, if snow falls, the mercury generally rises to 
30 , where it remains so long as the snow continues to fall; if after this the 
weather clears up, very severe cold weather may be expected. 

It will be observed that the barometer varies more in winter than in 
summer. It is at the highest in May and August; then in June, March, 
September and April. It is the lowest in November aud February; then in 
October, July, December and January. 

[These rules are from Dr. Brewer’s work called “ The Science of Familiar 
Things.”] 


543. Op the Different States of the Barometer. — Of the Fall of the 
barometer. — In very hot weather the fall of the Barometer indicates thun¬ 
der. Otherwise, the sudden fall of the barometer leads to the expectation 
of high wind. / 

In frosty weather the fall of the barometer denotes a thaw. 

If wet weather follow soon after the fall of the barometer, but littie ot 
«uch weather may be expected. 

In wet weather, if the barometer falls, expect much wet. 

In fair weather, if the barometer falls and remains low, expect much wet 
In a few days, and probably wind. 

The barometer sinks lowest of all for wind and rain together; next to 
that for wind, except it be an east or north-east wind. 


541. Of the Rise of the Barometer . — In winter the rise of the barometer 
presages frost. 

In frosty weather, the rise of the barometer presages snow. 

If fair weather happens soon after the rise of tho barometer, expect but 
little of it. 

In wet weather, if the mercury rises high and remains so, expect continued 
fine weather in a day or two. 

In wet weather, if the mercury rises suddenly very high, fine weather 
will not last long. * 

The barometer rises highest of all for north and west winds; for all other 
winds, it sinks. 


545. 7 he Barometer in an Unsettled State. If the motion of the mercury 
b® unsettled, eseect unsettled weather. 


v 


PNEUMATICS. 


±9 


li it stand at “ much rain,” and rise to “ changeable expert fail eatlier 
OT short continuance. 

If it stand at “ fair,” and fall to «* changeable ” expect foul wfcatb r. 

Its motion upwards indicates the approach of tine weather ; its motion 
‘townward indicates U»e approach of foul weather 

m rat is the ^46. Tiie Thermometer. — The Ther- 

Thermometcr , mometer * is an instrument to indicate the tem- 
and on what p . . T . 

principle is it perature oi the atmosphere. it is constructed 
constructed? on the principle that heat expands and cold 
contracts most substances. 


547. The thermometer consists of a capillary tube, closed at 
the top. and terminating downwards in a bulb. It is filled with 
mercury, which expands and fills the whole length of the tube or 
contracts altogether into the bulb, according to the degree of 
heat or cold to which it is exposed. Any other fluid may be 
used which is expanded by heat and contracted by cold, instead 
of mercury. Flg . 81 . 


548. On the side of the thermometer is a scale to 
indicate the rise and fall of the mercury, and conse¬ 
quently the temperature of the weather. 

What scale is 549. There are several different scales 
vloptedfor the applied to the thermometer, of which those 
of Fahrenheit, Reaumur, Delisle and Cel¬ 
sius, are the principal. The thermometer 
in common use in this country is graduated by Fahren- 
neit’s scale, which, commencing with 0, or zero, extends 
upwards to 212 degrees, the boiling point of water, and 
downwards to 20 or 80 degrees. The scales of Reau¬ 
mur and Celsius fix zero at the freezing point of water ; 
and that of Delisle at the boiling point. 


thermometer 
in this coun¬ 
try i 



What is the 550. Tiie Hygrometer. — The Ilygrom- 
Hygromete* ? e ter is an instrument for showing tiie degree 
of moisture in the atmosphere. 


* The word ' Thermometer” is from the Greek, and means «* a mea**r» 
pf heat.” “ Hygrometer ” means “ a measure of moistiue. ” 

13* 









L50 


NATURAL PHILOSOPHY. 


How is it con- 551- The hygrometer may be constructed of 
strutted? any material which dryness or moisture expands 
or contracts; such as most kinds of wood, catgi>t, twisted cord, 
the beard of wild oats, &c. It is sometimes also composed of a 
soi'e balanced by weights on one s : de, and a sponge, cr ot 1 er 
substance which readily imbibes moisture, on the other. 

552. By the action of the sun’s heat upon the surface of the 
earth, whether land or water, immense quantities of vapor are raised 
into the atmosphere, supplying materials for all the waiter which is 
deposited again in the various forms of dew, fog, rain, snow r , and 
hail. Experiments have been made to show the quantity of moist¬ 
ure thus raised from the ground by the heat of the sun. Dr. Wat¬ 
son found that an acre of ground, apparently dry and burnt up by 
the sun, dispersed into the air sixteen hundred gallons of water in 
the space of twelve hours. His experiment was thus made : He put 
a glass, mouth dow r nw r ards, on a grass-plot, on which it had net 
rained for above a month. In less than two minutes the inside was 
covered with vapor ; and in half an hour drops began to trickle dowm 
its inside. The mouth of the glass was 20 square inches. There 
are 1200 square inches in a square yard, and 4840 square yards in 
an acre. When the glass had stood a quarter of an hour, he wiped 
it with a piece of muslin, the weight of w’hich had been previously 
ascertained. When the glass had been wiped dry, he again weighed 
the muslin, and found that its weight had increased six grains by 
the w'ater collected from 20 square inches of earth ; a quantity equa 1 
to 1000 gallons, from an acre, in 12 hours. Another experiment, 
after rain had fallen, gave a much Larger quantity. 

553. When the atmosphere is colder than the earth, the vapor 
which arises from the ground, or a body of water, is condensed and 
becomes visible. This is the way that fog is produced. When the 
earth is colder than the atmosphere, the moisture in the atmosphere 
condenses in the form of dew', on the ground, or other surfaces. 
Clouds are nothing more than vapor condensed by the cold of the 
upper regions of the atmosphere. Rain is produced by the sudden 
cooling of large quantities of watery vapor. Snow and hail are 
produced in a similar manner, and differ from rain only in the de* 
gree of cold which produces them. 

What is the -554. TlIE DlVER ; S BELL OR DlVING-BELL. 

Vivmg-bell , — The Diving-bell is a large vessel shaped like 

and on what . ° . . 1 

principle is it an inverted goblet, in which a person may 
constructed ? safely descend to great depths in the water. 
It is constructed on the principle of the impenetrability of 
air. 


PNEUMATICS. 


151 


555. It has already been stated that air, being a material sub 
stance, possesses all the given essential properties of matter, and 
among them the property of impenetrability. The weight of the 
air giving it a pressure in every direction, or the property of fluidity, 
it penetrates and Alls all things around us, unless by mechanical 
means it be carefully excluded. An open vessel, of whatever kind, 
is always full either of air or of some other substance, and unless 
the air is first permitted to escape no other substance can take the 
place of the air. 

55G. If a tumbler be inverted and immersed in water, the water 
will not rise in the tumbler, because the air in the tumbler fills it. 
If the tumbler be inclined so as to let the air ascend in obedience to 
the laws of the equilibrium of fluids, the water will rush in and dis¬ 
place the air, while the lighter air, ascending, rises to the surface of 
the water. If this experiment be made with a bottle, the air will 
rise in bubbles with a gurgling sound. The same experiment may be 
made with a tube closed at one end by the finger; the water will not 
enter the tube until' by the removal of the finger the air be permitted 
to escape. It is on this principle that the diving-bell is constructed 

, . 7 557. Fig. 82 represents a 

Explain the con- ... , „ _ . „ 

struction of the diving-bell. It consists of a 

diving-bell by large heavy vessel, formed 
Fig. 82. like a bell (but may be made 

of any other shape), with the mouth open. It 
descends into the water with its mouth down¬ 
wards. „ The air within it having no outlet, 
it is compelled by the order of specific grav¬ 
ities to ascend in the bell, and thus (as water 
and air cannot occupy the same space at the 
same time) prevents the water from rising 
in the bell. A person, therefore, may de¬ 
scend with safety in the bell to a great depth 
in the sea, and thus recover valuable articles 
that have been lost. A constant supply of 
fresh air is sent down, either by means of 
barrels, or by a forcing-pump. In the Fig. 

P represents the bell with the diver in it.. C is a bent metal- 
tube attached to one side and reaching the air within; and 
P is the forcing-pump through which air is forced into the bell. 
The forcing-pump is attached to the tube by a joint at D. When 
the bell descends to a great depth, the pressure of the water 








NATURAL PHILOSOPHY. 


JL&2 


//r«? is water 
raised in a com¬ 
mon pump ? 
How high map 
water be raised 
by a common 
pump ? 


condenses tlie air within the bell, and causes the water to ascend 
in the bell. This is forced out by constant, accessions of fresh 
air, supplied as above mentioned. Great care must be taken 
that a constant supply of fresh air is sent down, otherwise the 
lives of those within the bell will be endangered. The heated 
and impure air is allowed to escape through a stop-cock in the 
upper part of ihe bell. 

- 558. The Common Water Pump.— 

Water is raised in the common pump by 
means of the pressure of the atmosphere 
on the surface of the water. A. vacuum 
being produced by raising the piston or 
pump-bex,* the water below is rig. 83. 
forced up by the atmospheric pressure, on the 
principle of the equilibrium of fluids. On this 
principle the water can be raised only to the 
height of about thirty-three feet, because the 
pressure of the atmosphere will sustain a column 
of water of that height only. 

559. Fig. 83 represents the common 
83 P um P> improperly called the sucking- 
pump. The body consists of a large tube, 
or pipe, the lower end of which is immersed in the 
water which it is designed to raise. P is the piston, 

V a valve t in the piston, which, opening upwards, 
admits the water to rise through it, but prevents its 
return. Y is a similar valve in the body of the 


& 


-V 


Ch 


B 


* In order to produce such a vacuum, it is necessary that the piston oi 
box should be accurately fitted to the bore of the pump ; for, if the air 
above the piston has any means of rushing in t.> fill the vacuum, as it is 
produced by the raising of the piston, the water will not ascend The pis¬ 
ton is general’/ worked by a lever, which is the handle of the pump, not 
represented in the figure. 

t A valve is a lid, or cover, so contrived as to open a communication in 
one way and close it in the other. Valves are made in different ways, 
according to the use for which they are intended. In the common pumj 
they are generally made of thick leather partly covered with wood Tn 
the air-pump they are made of oiled silk, or thi:« leather softened with 
oil. The clapper of a pair of bellows is a familiar specimen of a valv® 
the valves of a pump are commonly called boxts 

















PNEUMATICS. 


153 


pump, below the piston. When the pump is not in action, the 
valves are closed by their own weight; but when the piston is 
raised it draws up the column of water which rested upon it 
producing a vacuum between the piston and the lower valve Y 
The water below immediately rushes through the lower valve 
and fills the vacuum. W T hen the piston descends a second time, 
the water in the body of the pump passes through the valve 
V, and on the ascent of the piston is lifted up by the piston, 
and a vacuum is again formed below, which is immediately 
filled by the water rushing through the lower valve Y. In 
this manner the body of the pump is filled with water, until it 
reaches the spout S, where it runs out in an uninterrupted stream. 

560. In the description here given of the common pump, as 
well as in the figure, it will be observed that the common form 
of the handle of the pump is not noticed. The handle of the pump 
is merely a lever of the first kind; the fulcrum is the pin which 
attaches it to the pump, and the iron rod connected with the 
upper valve of the pump is raised or depressed by means of the 
handle. 


5G1. Although water can be raised by the atmospheric pressure 
only to the height of thirty-three feet above the surface, the com¬ 
mon pump is so constructed that after the pressure of the atmos¬ 
phere has forced the water through the valve in the body of the 
pump, and the descent of the piston has forced it through the valve 
in the piston, it is lifted up, when the piston is raised. For this 
reason, this pump is sometimes called the lifting pump. The dis¬ 
tance of the upper valve from the surface of the water must never 
exceed thirty-two feet; and in practice it must be much less. 


How does the 
Forci ng-pump 
differ from the 
common pump ? 


562. Tiie Forcing-pump. The Forcing- 
pump differs from the common pump in 
having a forcing power added, to raise the 
water to any desired height. 


563. Fig. 84 represents the forcing-pump. Tho 

Explain ^dy an j i owe r valve V are similar to those in the 
tig. fc4. J 

common pump. The piston P has no valve, but is 
rolid when, therefore, the vacuum is produced above the 


t 


154 NATURAL PHILOSOPHY. 


Fig. 84 



lower valve, the water, on the descent 
of the piston, is forced through the tube 
into the reservoir or air-vessel R, where 
it compresses the air above it. The air, 
by its elasticity, forces the water out 
through the jet J in a continued stream, 
and with great force. It is on this prin¬ 
ciple that fire-engines are constructed. 

Sometimes a pipe with a valve in it is 
substituted for the air-vessel; the water 
is then thrown out in a continued stream, 
force. 


Mow is the 
t'/re-engine 
instructed ? 


564. Tiie Fire-engine consists of two forcing- 
pumps, worked successively by the elevation and 
depression of two long levers of the second kina, 
called “ Brakes.” 


Fig. 86. 



. , . The Air-pump.— The Air-pump is 

Whai ts the . . . . f 

Air-pump, and a machine constructed on the principle of the 

on what prin- elasticity of the air, for the purpose cf ex- 
uj)le is it con- ^ 

structcd ? hausting the air from a vessel prepared for 


the purpose. This vessel is called a receiver, 
and is made of glass, in order that the effects of the remova,! 
of the air may be seen. 


566. Air-pumps are made in a great variety of forms; but al 
are constructed on the principle tha*, when any portion of confine* 
















PNEUMATICS. 


155 


air is removed, the residue, immediately expanding, by its elasticity 
fills the space occupied by the portion that has been withdrawn. 

Explain the con- 567. I)’ig.-86 represents a single-barrel air 
struction of the pump, used both for condensing and exhausting. 

% A D is the stand or platform of the instru¬ 
ment, which is screwed down to the table by 


air-pump 
Fig . 86. 


nO> 


Fig. 86. 



means of a clamp, underneath, 
which is not represented in the 
figure. II is the glass vessel, 
or bulbed receiver, from which 
the air is to be exhausted. P 
is a sol*d piston, accurately fit¬ 
ted to the bore of the cylinder, 
and H the handle by which it 
is moved. The dotted line T 
represents the communication 
between the receiver B and the 
barrel B ; it is a tub hrough 

which the air, entering at the opening I, on the plate of the 
pump, passes into the barrel through the exhausting valve e v. 
C v is the condensing valve, communicating with the barrel B 
by means of an aperture near e, and opening outwards through 
the condensing pipe p. 

Explain the op- 568 ‘ The °P eration of the pump is as follows • 
eration of the The piston P being drawn upwards by the han¬ 
dle H, the air in the receiver B, expanding bv 
its elasticity, passes by the aperture I through 
the tube T, and through the exhausting valve e v, into the bar¬ 
rel. On the descent of the piston, the air cannot return through 
that valve, because the valve opens upwards only: it must, 
therefore, pass through the aperture by the side of the valve, 
and through the condensing valve c v, into the pipe p , where it 
passes out into the open air. It cannot return through the con¬ 
densing valve c v, because that valve opens outward s only. By 
continuing this operation, every ascent and descent of the piston 
P must render the air within the receiver B. more and more 


air-pump by 

Fig. 90 . 













156 


NATURAL PHILOSOPHY. 


rare, until its elastic power is exhausted. Tne receiver is then 
said to be exhausted; and, although it siiii contains a small 
quantity of air, yet it is in so rare a state that the space within 
the receiver is considered a vacuum. 


569. From this statement it will appear that a perfect vacuum 
can never be obtained by the air-pump as at present constructed. 
But so much of the air within a receiver may be exhausted that the 
residue will be reduced to such a degree of rarity as to subserve 
most of the practical purposes of a vacuum. The nearest approach 
made to a perfect vacuum is the famous experiment of Torricelli, 
which has been explained in No. 530. That would be a perfect 
vacuum, were there not vapor rising from the mercury. 


570. From the explanation which has been 

ofrlcSnS § iven of the °P erat!on of this air-pump, it will 
by means of the readily be seen that, by removing the receiver 

pump which has an d scre wing any vessel to the pipe the 
been described ? . , , , . . . . 

air may be condensed in the vessel, lhus the 

pump is made to exhaust or to condense, without alteration. 

vVbiai is a con- 571. Air-pumps in general are not adapted 
densing syr- for condensation; that office being performed by 
tn S e • an instrument called 11 a condensing syringe?' 

which is an air-pump reversed , its valves being so arranged as 
to force air into a chamber, instead of drawing it out. For 
this purpose, the valves open inwards in respect to the chamber, 
while in air-pumps they open outwards. 


572. A guage, constructed on the principle of the barometer, ia 
sometimes adjusted to the air-pump, for the purpose of exhibiting 
the degree of exhaustion. 


How does the ^73. The double air-pump differs from tho 
double air-pump single air-pump, in having two barrels and two 

differ from the pistons; which, instead of being moved by the 
single 1 f J 

hand, are worked by means of a toothed wheel, 

playing in notches of the piston-rods. 


Fig. 87 represents an air-pump of a different construction 
In tliis pump the piston is stationary, while motion is given to the 
barrel by means of the lever II. Tho barrel is kept in a prow 
position by means of polished steel ^uidey. 


PNEUMATICS. 


15? 



574. By means of the air-pump many interesting experiments 
may be performed, illustrating the gravity, elasticity, fluidity, and 
inertia of air. 

575. Experiments Illustrating the Gravity of Air. — Having 
adjusted the receiver to the plate of the air-pump, exhaust the air 
and the receiver will be held firmly on the plate. The force which 
confines it is nothing more than the weight of the external air 
which, (having no internal pressure to contend with, presses with a 
force of nearly fifteen pounds on every square inch of the external 
surface of the receiver. 

576 The exact amount of pressure depends on the degree of ex¬ 
haustion, being at its maximum of fifteen pounds when there is a 
perfect vacuum. On readmitting the air, the receiver may be readily 
*emoved. # 


What are the 
Magdeburgh 
Cups, and what 
do they illus¬ 
trate ? 


577. The Magdeburgh Cups, or Hemi¬ 
spheres. — Fig. 88 represents the Magdeburgh 
Cups, or Hemispheres. They consist of two hol¬ 
low brass cups, the edges of which are accu¬ 
rately fitted together. They each have a handle, 


* The air is readmitted into the receiver by turning a screw which is in¬ 
erted into the receiver, in which there is ar aperture, through which th* 
a>torual air rushes with considerable force. 

14 
































158 


NATURAL PHILOSOPHY. 



to one of which a stop-cock is fitted. The stop* 
cock, being attached to one of the cups, is to be 
screwed to the plate of the air-pump, and left 
open. Having joined the other cup to that on 
the pump, exhaust the air from within them, 
turn the stop-cock to prevent its re admission, 
and screw the handle that had been removed to 
the stop-cock. Two persons may then attempt 
to draw the cups asunder. It will be found that 
great power is required to separate them; but, 
on readmitting the air between them, by turning 
the cock, they will fall asunder by their own 
weight. When the air is exhausted from within them, the press¬ 
ure of the surrounding air upon the outside keeps them united. 
This pressure being equal to a pressure of fifteen pounds on every 
square inch of the surface, it follows that the larger the cups ; 
or hemispheres, the more difficult it will be to separate them. 

578. The Magdeburgh Cups derive their name from the city 
the experiment was first attempted. Otto Guericke con¬ 
ed two hemispheres which, when the air was exhausted, were 




held together by a force of about three-fourths of a ton. Fio\ 89 
shows the manner in which such an experiment may be tried. ° 

® What principle b/9. The Hand-glass. — Fig. 

does the Hand- 90 is nothing more than a tuni- 
* bier, open at both ends, with 

the top and bottom ground smooth, so as to fit 
the brass plate of the air-pump. Placing it 
upon the plate, cover it closely with the palm 
of the hand, and work the pump. Tbo a : i 












PNEUMATICS. 


159 


Fig. 31. 



What does the 
India-rubber 
Glass show ? 


witbin the glass being thus exhausted, the hand will be pressed 
down by the weight of the air above it: on readmitting the air 
the hand may be easily removed. 

i What principle 580 ' TuE Bladdek-olass.— 
is illustrated by Fig. 91 is a bell-shaped glass, 

v/ass i Bladder ~ covered with a piece of blad¬ 
der, which is tied tightly around 
its neck. Thus prepared, it may be screwed 
to the plate of the air-pump, or connected with 
it by means ©f an elastic tube. On exhausting 
the air from the glass, the weight of the external air on the 
bladder will burst it inwards, with a loud explosion. 

581. The India-rubber Glass. 
— Fig. 92 is a glass similar to 
the one represented in the last 
figure, covered with india-rubber. The same 
experiments may be made with this as were 
mentioned in the last article, but with different results. Instead 
of bursting, the india-rubber will be pressed inwards the whole 
depth of the glass. 

What is Ulus- 582. The Fountain-glass and Jet. — Fig. 
t.rated by means S3 represents the jet, which is a small brass 
of the Fountain- tube. Fig. 94 is the fountain-glass. The ex- 
periment with these instruments is designed to 
Fig. 93. show the pressure of the atmosphere oh ri &- 94 - 
the surface of liquids. Screw the straight 
jet to the stop-cock, the stop-cock to the 
fountain-glass, with the straight jet inside 
of the fountain-glass, and the lower end of 
the stop-cock to the plate of the air-pump, 
and then open the stop-cock. Having ex¬ 
hausted the air from the fountain-glass, close the stop- 
sock, remove the glass from the pump, and, immersing 
it in a vessel of water, open the stop-cock. The pressure 
of the air on the surface of the water will cause it to rush up 
into the glass like a fountain. 











160 


NATURAL PHILOSOPHY. 



How are the 583. Pneumatic Scales FOR WEIGHING AlR.- 
Pneumatic Pig. 95 represents the flask, Fip. 95. 

Scales used ? or g] asa vessel and scales for 

weighing air. Weigh the flask when full 
of air; then exhaust the air and weigh the 
flask again. The difference between its 
present and former weight is the weight of 
ihe air that was contained in the flask, 
nr, . • • 584. Tiie Sucker. — A 

Vv hat 'princi¬ 
ple does “ the circular piece of wet leather, with a string 

Sucker ” Ulus- attached to the centre, being pressed upon a 
smooth surface, will adhere with considerable 
tenacity, when drawn upwards by the string. The string in 
this case must be attached to the leather, so that no air can pass 
under the leather. 

What is the 585. The Mercurial or Water Tube.— 
object of the Exhaust the air from a glass tube three feet 
Mercurial or j on fitted with a stop-cock at One end, and then 
immerse it in a vessel containing mercury or 
w.ater. On turning the stop-cock, the mercury will rise to the 
height of nearly thirty inches; or, if immersed in water, the 
water will rise and fill the tube, and would fill it were it thirty 
feet long. This experiment shows the manner in which water 
is raised to the boxes or valves in common water-pumps. 


How is the elas- 


586. Experiments showing tiie Elasticity 


ticity of the air of the Air. — Place an india-rubber bag, or a 
illustrated l bladder, partly inflated, and tightly closed, un¬ 
der the receiver, and, on exhausting the air, the air within the 
bag or bladder, expanding, will fill the bag. On readmitting 
the air, the bag will collapse. The experiment may also be 
made with some kinds of shrivelled fruit, if the skin be sound. 
The internal air, expanding, will give the fruit a fresh and plump 
appearance, which will disappear on the readmissiou of the air 

587. The same principle may be illustrated by th« india- 




PNEUMATICS. 


161 


ruober and bladder glasses, if they have stop-cocks to confine < 
the air. 

588. A small bladder partly filled with air may be sunk in a 
vessel of water by means of a weight, and placed under the 
receiver. On exhausting the air from the receiver, the air in 
the bladder will expand, and, its specific gravity being thus 
diminished, the bladder with the weight will rise. On read¬ 
mitting the air, the bladder will sink again. 

How can the ^89 . Air contained in Water and in Wood. 

presence of air — Place a vessel of water under the receiver, and, 
Reeled* ^ ^ ° n exhaustin g the air fr° ra the receiver, the air 
in the water, previously invisible, will make its 
appearance in the form of bubbles, presenting the semblance 
of ebullition. 

590. A piece of light porous wood being immersed in tha 
water below the surface, the air will be seen issuing in bubbles 
from the pores of the wood. 

Explain ,/te prin- 591 ' TuE Pneumatic Balloon.— 
ciple of the Pneu - Fig. 96 represents a small glass bal- 
matic Balloon. loon, w ith its car immersed in a jar 
of water, and placed under a receiver. On exhaust¬ 
ing the air, the air within the balloon, expanding, gives 
it buoyancy, and it will rise in the jar. On readmit¬ 
ting the air, the balloon will sink. 

692. The experiment may be performed without the 
air-pump by covering the jar with some elastic sub¬ 
stance, as india-rubber. 13y pressing on the elastic 
covering with the finger, the air will be condensed, the 
water will rise in the balloon, and it will sink. On removing 
the pressure, the air in the balloon, expanding, will expel part 
of the water, and the balloon will rise. This is the more conve¬ 
nient mode of performing the experiment, as it can be repeated 
at pleasure without resort to the pump. 

593. The following is a full explanation : — The pressure on 
the cop of the vessel first condenses the air between the covei 

14* 


Fig. 9e 




NATURAL PHILOSOPHY. 


102 


and the surface of the water; this condensation presses upon 
the water below, and, as this pressure affects every portion of 
the water throughout its whole extent, the water, by its upward 
pressure, compresses the air within the balloon, and makes room 
for the ascent of more water into the balloon, so as to alter the 
specific gravity of the balloon, and cause it to sink. As soon 
as the pressure ceases, the elasticity of the air in the balloon 
drives out the lately-entered water, and, restoring the former 
lightness to the balloon, causes it to rise. If, in the commence¬ 
ment of this experiment, the balloon be made to nave a specific 
gravity too near that of water, it will not rise of itself, 
after once reaching the bo+*om, because the pressure of the 
water then above it will perpetuate the condensation of the air 
which earned it to descend. It may* even then, however, be 
made to rise, if the perpendicular height of the water above it 
be diminished by inclining the vessel to one side. 

594. This experiment proves many things ; namely : 

First. The materiality of air, by the pressure of the hand' on the 
top being communicated to the water below through the air in the 
upper part of the vessel. 

Secondly. The compressibility of air , by what happens in the 
globe before it descends. 

Thirdly. The elasticity , or elastic force of air, when the water is 
expelled from the globe, on removing the pressure. 

Fourthly. The lightness of air , in the buoyancy of the globe. 

Fifthly. It shows that the pressure of a liquid is exerted in all direo 
tions, because the effects happen in whatever position the jar be 
held. 

Sixthly. It shows that pressure is as the depth, because less press¬ 
ure of the hand is required the further the globe has descended in 
the water. 

Seventhly. It exemplifies many circumstances of fluid support. 
A person, therefore, who is familiar with this experiment, and can 
explain it, has learned the principal truths of Hydrostatics and 
Pneumatics. 

595. The Pneumatic Balloon also exhibits the principle on which 
the well-known glass toy, called the Cartesian Devil, is constructed ; 
and it may be thus explained: Several images of glass, hollow 
within, and each having a small opening at the heel by which water 
may pass in and out, may be made to manoeuvre m a vessel rf 
water. Place them in a vessel in the same manner with the bal 
©on, out, by allowing different quantities of water to enter the 


PNEUMATICS. 


lt'3 


apertures in the images, cause them to differ a little from one 
another in specific gravity. Then, when a pressure is exerted ma 
the cover, the heaviest will descend first, and the others follow in 
the order of their specific gravity ; and they will stop or return to 
the surface in reverse order, when the pressure ceases. A person 
exhibiting these figures to spectators who do not understand them, 
while appearing carelessly to rest his hand on the cover of the ves¬ 
sel, seems to have the power of ordering their movements by his 
will. If the vessel containing the figures be inverted, and the cover 
be placed over a hole in the table, through which, unobserved, press¬ 
ure can be made by a rod rising through the hole, and obeying the 
foot of the exhibiter, the most surprising evolutions may be pro¬ 
duced among the figures, in perfect obedience to the word of com¬ 
mand. 


C7 

Exhaustin 
Syringe ? 


Fig. 97. 


Experiments with Condensed Air.— 
use of theCon- The Condensing and Exhausting Syringe.— 
densins and The Condensing Syringe is the air-pump reversed. 

The Exhausting Syringe is the simple air-pump 
without its plate or stand. These implements 
are used respectively with such parts 
of the apparatus as cannot conveniently 
be attached to the air-pump, and as 
an addition to such pumps as do not 
perform the double office of exhaustion 
and condensation. In some sets of 
apparatus the condensing and exhaust¬ 
ing syringes are united, and are made 
to perform each office respectively, by 
merely reversing the part which con¬ 
tains the valve. 

For what purpose 597 ‘ The Air ' 
is the Air - cham - chamber.— The air- 

^er used ? chamber, Fig. 97, is 

a hollow brass globe prepared for the reception of a stop-cock, 
and is designed for the reception of condensed air. It is made 
in different forms in different sets, and is used by screwing it to 
ft condensing p imp or a condensing syringe. 

^ 598. Straight and Revolving Jets from 

.riyle tj r pneur Condensed Air.-- Fill the air-chamber (Fig 



164 


NATURAL PHILOSOPHY. 


Fig. 99. 


, . 97) partly with water, and then condense the 

trnted by the air. Then confine the air by turning the cock ; 

straight and a ft cr which, unscrew it from the air-pump, and 

i evoking jets? fccrew on the straight or the revolving jet. Then 
open the stop-cock, and the water will be thrown from the 
chamber in the one case in 
a straight continued stream, 
in the other in the form of 

a wheel. Figs. 98 and 99 _ 

represent a view of the 

straight and the revolving jets. In the revolving jet 
the water is thrown from two small apertures made at 
each end on opposite sides, to assist the revolution. The 
circular motion is caused by the reaction of the water on the 
opposite sides of the arms of the jets; for, as the water is forced 
into the tubes, it exerts an equal pressure on all sides of the 
tubes, and, as the pressure is relieved on one side by tho jet- 
hole, the arm is caused to revolve in a contrary direction This 
experiment, performed with the straight jet, illustra tho 
principle on which “ Hero’s ball” and “Hero’s fountate ” are 
constructed. 

Explain the 599. The Principle of TiiE Air-gun. --With 
prinrtple of the air-chamber, as in the last experiy/mts, a 
the Air-gun. sma q brass cylinder or gun-barrel, Fig. 1»»0, may 
be substituted for the jets, and loaded with a small shot pig. 100 
or paper ball. On turning the cock quickly, the con¬ 
densed air, rushing out, will throw the shot to a consider¬ 
ate distance. In this way the air-gun operates, an 
apparatus resembling the lock of a gun being substituted 
for the stop-cock, by which a small portion only of the 
condensed air is admitted to escape at a time; so that 
the chamber, being once filled, will afford two or three 
discharges. The force of the air-gun has never been eqial to 
mere than a fifteenth of the force of a common charge of powder, 
and the loudness of the report made in its discharge is always 
as great in proportion to it; force as that of the common gun. 


hj| 


dozen 









PNEUMATICS. 


m 


In weighing 
atr what must 
always he' 
taken into the 
accountJ 


600, Condensed air may be weighed in the 
air-chamber, but, in estimating its weight, the 
temperature of the room must always be taken 
into consideration, as the densiiy of air is ma¬ 
terially affected by heat and cold. 


Fig. 101 


Fig. 102. 


What does the 601. ^ XPERIMENTS showing the Inertia of 
Guinea and Air. — The Guinea and Feather Drop. — The 
leather Drop inertia of air is shown by the guinea and feather 
drop, exhibiting the resistance which the ail* 
opposes to falling bodies. This apparatus is made in different 
lornia, some having shelves on which the 
guinea and feather rest, and, when the air is 
exhausted, they are made to fall by the turn¬ 
ing of a handle. A better form is that repre¬ 
sented in Fig. 101, in which the guinea and 
feather (or a piece of brass substituted for the 
guinea) are enclosed, and the apparatus being 
screwed to the plate of the pump, the air is 
exhausted, a stop-cock turned to prevent the 
reiidmission of the air, and the apparatus being 
then unscrewed, the experiment may be repeatedly 
shown by one exhaustion of the air. It will then 
appear that every time the apparatus is inverted the 
guinea and the feather will fall simultaneously. The 
two forms of the guinea and feather drop are ex¬ 
hibited in Figs. 101 and 102, one of which, Fig. 101, is fur¬ 
nished with a stop-cockthe other, Fig. 102, with shelves. 

What prin- 602. Experiments SHOWING THE FLUIDITY OF 

vijde is explain- Air. — Tn e Weight-lifter. —The upward press- 

Ihewei^kl* U1 e t ^ ic a * r » one ^he P ro P er ti es °f its fluidity, 
liftyrl* 3 may be exhibited by an apparatus called the 


* Most sets of philosophical apparatus are furnished with stop-cocks 
and elastic tubes, fur the purpose of connecting the several parts with the 
pump, or with one another. In selecting the apparatus, it is important 
to have the screws of the stop-cocks and of all the apparatus of similar 
thread, in order that every article may subserve as many purposes as pos¬ 
sible. This precaution is suggested by economy, as well as by convenience 









166 


NATURAL PHILO SOPIIY. 


Pig. lOd. 



weight-lifter, made in different forms, but all 
on the same principle. The one represented 
in Fig. 103 consists of a glass tube, of large 
bore, set in a strong case or stand, sup¬ 
ported by three legs. A piston is accu¬ 
rately fitted to the bore of the tube, and a 
hook is attached to the bottom of the piston, 
from which weights are to be suspended. 

One end of the elastic tube is to be screwed 
to the plate of the pump, and the other 
end attached to the top of this instrument. 

The air being then exhausted from the tube, the weights will be 
raised the whole length of the glass. The number of pounds 1 
weight that can be raised by this instrument may be estimated 
by multiplying the number of square inches in the bottom of 
the piston by fifteen. 

Explain the 603. The Pneumatic Shower-bath. — On the 
Pneumatic principle of the upward pressure of the air the 

Shower-bath. p neulJla ti c shower-bath is constructed. It con¬ 
sists of a tin vessel perforated with holes in the bottom for the 
shower, and having an aperture at the top, which is opened or 
closed at pleasure by means of a spring-valve. [Instead of the 
spring-valve, a bent tube may be brought round from the top 
down the side of the vessel, with an aperture in the tube below 
the bottom of the vessel, which may be covered with the thumb.] 
On immersing the vessel thus constructed in a pail of water, 
with the valve open, and the tube (if it have one) on the outside 
of the pail, the water will fill the vessel. The aperture then 
being closed with the spring or with the thumb, and the vessel 
being lifted out of the water, the upward pressure of the aii 
will confine the water in the vessel. On removing the thumb 
or opening the valve, the water will descend in a shower, until 
the vessel is emptied. 

What two 604. Miscellaneous Experiments depending 

properties of on two or more of the Properties of Air.-' 




PNEUMATICS. 


m 


air are ilbts- The BoLT-nEAD AND J ar. — Fig. 104, a glass 
^mcansqf the g^°^ e a long neck, called a bolt-head (or 

Bolt-head and any long-necked bottle), partly filled with water 
^ ar - is inverted in a jar of water (colored with a few 

drops of red ink or any coloring matter, in order 
that the effects may be more distinctly visible), and 
placed under the receiver. On exhausting the air in 
the receiver, the air in the upper part of the bolt- 
head, expanding, expels the water, showing the elas¬ 
ticity of the air. On readmitting the air to the 
receiver, as it cannot return into the bolt-head, the 
pressure on the surface of the water in the jar forces 
the water into the bolt-head, showing the pressure 
of the air caused by its weight. The experiment 
may be repeated with the bolt-head without any 
water, and, on the readmission of the air, the water will nearly 
fill the bolt-head, affording an accurate test of the degree of 
exhaustion. 


Fig. 104. 



605. Tiie Transfer of Fluids from one 
Vessel to Another. — The experiment maybe 
made with two bottles tightly closed. Let one 
be partly filled with water, and the two con¬ 
nected by a bent tube, connecting the interior of 
the empty bottle with the water of the other, and 
extending nearly to the bottom of the water. On exhausting 
the air from the empty bottle, the water will pass to the other 
and, on readmitting the air, the water will return to its original 
position, so long as the lower end of the bent tube is below the 
surface. 


What two 
principles are 
concerned in 
the transfer of 
fluids from 
one vessel to 
another 1 


^ ^ . 606. Experiments with the Siphon. — Close 

merits are^er- the shorter end of the siphon with the finger or 
formed with with, a stop-cock, and pour mercury or water into 
the siphon ? l on ger side. The air contained in the shorter 

side will prevent the liquid from rising in the shorter side. 
But, if the shorter end be opened, so as to afford free passage 







103 


NATURAL PHILOSOPHY. 


outwards for the air, the fluid will rise to an equilibrium m 
both arms of the siphon. 

607. Pour any liquid into the longer arm of the siphon until 
vne shorter arm is filled. Then close the shorter end, tc pre¬ 
vent the admission of the air; the siphon may then be turned 
in any direction and the fluid will not run out, on account of 
the pressure of the atmosphere against it. But, if the shorter 
end be unstopped, the fluid will run out freely. 

What effect is 008. Air essential to Animal Life. — If 
produced on an , , . . . 1( . , 

animal placed an animal be placed under the receiver, and the 

under an ex- air exhausted, it will immediately droop, and, if 

hausted re- ^Im air be not speedily readmitted, it will die. 
ceivert r J 

. f 609. Air essential to Combustion. — Place 

shown that air a lighted taper, cigar, or any other substance that 

is essential to w ill produce smoke, under the receiver, and ex- 

combustion? h^nst the air; the light will be extinguished, and 

Ihe smoke will fall, instead of rising. If the air be readmitted, 

the smoke will ascend. 


What effect is 
produced on 
ether under an 
exhausted re¬ 
ceiver ? 


610. The Pressure of tiie Air retards 
Ebullition. 3 ^ —Ether, alcohol, and other distilled 
liquors, or warm water, placed under the receiver, 
will appear to boil when the air is exhausted. 

611. The existence of many bodies in a liquid 
the pressure of f° rm depends on the weight or pressure of the 
the air on the atmosphere upon them. The same force, like¬ 
wise, prevents the gases which exist in fluid and 
solid bodies from disengaging themselves. If, by 

rarefying the air, the pressure on these bodies be diminished, 
they either assume the form of vapors, or else the gas detaches 
itself altogether from the other body. The following experi¬ 
ment proves this: Place a quantity of lukewarm water, milk 
or alcohol, under a receiver, and exhaust the air, and the liquid 


What effect, has 


form of 
bodies ? 


* Ebullition. — The operation of boiling. The agitation of liquor by 
which throw? it up into bubble?. 


PNEUMATICS. 


109 


fill either pass off in vapor, or will have the appearance of 
ooiling. 

What vxperi- ®12. ex P er i inen ^ to prove that the pressure 
merit shores of the atmosphere preserves some bodies in the 
that the liquid liquid form may thus be performed. Fill a long 

bodies°(s v ^ a *’ or a tu ^ e c ^ ose( ^ at one end, with water, and 

pendent on invert it in a vessel of water. The atmospheric 

atmospheric pressure will retain the water in the vial. Then, 

pressure ? £ 

by means of a bent tube, introduce a few drops 
of sulphuric ether, which, by reason of their small specific 
gravity, will ascend to the top of the vial, expelling an equal 

bulk of water. Place the whole under the receiver, and ex- 

naust the air, and the ether will be seen to assume the gaseous 
form, expanding in proportion to the rarefaction of the air 
under the receiver, so that it gradually expels the water from 
the vial, and fills up the entire space itself. On readmitting 
the a«r, the ether becomes condensed, and the water will re¬ 
ascend into the vial. 


,_r 613. A simple and interesting experiment con 

now may r . 

water he frozen nected with the science of chemistry may thus be 
under a rt- performed by means of the air-pump. A watch- 
Ulltr - glas&, containing water, is placed over a small 

vessel containing sulphuric acid, and put under the bulbed 
"eceiver. When the air is exhausted, vapor will freely rise 
from the water, and be quickly absorbed by the acid. An 
intense degree of cold is thus produced, and the water will 
freeze. 


614. In the above experiment, if ether be used instead of the 
acid, the ether will evaporate instead of the water, and, in the 
process of evaporation, depriving the water of its heat, the 
water will freeze. These two experiments, apparently similar 
m effects, namely, the freezing of the water, depend upon two 
different principles which pertain to the science of chemistry. 


What is the 
Pneumatic 
Paradox ? 


Nil5. The Pneumatic Paradox. — An inter¬ 
ring experiment, illustrative of the pneumatic 


15 


170 


NATURAL PHILOSOPHY. 


paracbz, may be thus performed: Pass a small open tube (us 
a piece of quill) through the centre of a circular card two or 
three inches in diameter, and cement it, the lower end passing 
down, and the upper just even with the card. Then pass a pin 
through the centre of another similar card, and place it on 
the former, with tne pin projecting into the tube to prevent 
the upper card from sliding off. It will then be impossible 
to displace the upper card by blowing through the quill, 
on account of the adhesion produced by the current passing 
between the discs. On this principle smoky chimneys have 
j®en remedied, and the office of ventilation more effectually 
performed. 


What is 
Wind ? 


61G. Wind. —Wind is air put in motion. 


617. There are two ways in which the motion 
of the air may arise. It may be considered as 
an absolute motion of the air, rarefied by heat 
and condensed by cold; or it may be only an 
apparent motion, caused by the superior velocity 
of the earth in its daily revolution. 


•'"i what two 
«>u,ys mav the 
.iotion of the 
air be ex¬ 
plained ? 


618. When any portion of the atmosphere is heated it becomes 
rarefied, its specific gravity is diminished, and it consequently 
rises. The adjacent portions immediately rush into its place, to 
restore the equilibrium. This motion produces a current which 
jushes into the rarefied spot from all directions. This is what 
we call wind. 


H ^ 619. The portions north of the rarefied spot 

wind caused ? P r °duce a north wind, those to the south produce 
a south wind, while those to the east and west 
;n like manner, form currents moving in opposite directions 
At the rarefied spot, agitated as it is by winds from all direc* 
dons, turbulent and boisterous weather, whirlwinds, hurricanes, 
rain, thunder and lightning, prevail. This kind of weather 
occurs most frequently in the torrid zone, where the heat is 
greatest. The air, being more rarefied there than in any otho 


rNKCMATIOB. 


171 


part d? the globe, is lighter, and, consequently, ascends; that 
about thd polar regions is continually flowing from the poles to 
the equator, to restore the equilibrium; while the air rising 
from the equator flows in an upper current towaids th£ poles, 
so that the polar regions may not be exhausted. 

What wind 620. ^ re S u ^ ar east w i n( l prevails about the 

prevails in the equator, caused in part by the rarefaction of the 

equatorial air produced by the sun in his daily course from 
regions? 1 . . . , . . . , 

east to west, ihis wind, combining with that 

from the poles, causes a constant north-east wind for about thirty 

degrees north of the equator, and a south-east wind at the 

same distance south of the equator. 

621. From what has now been said, it appears that there is a 
circulation of air in the atmosphere; the air in the lower strata 
flowing from the poles to the equator, and in the upper strata 
flowing back from the equator to the poles. It may here be re¬ 
marked, that the periodical winds are more regular at sea than on 
the land ; and the reason of this is, that the land reflects into the 
atmosphere a much greater quantity of the sun’s rays than the 
waiter, therefore that part of the atmosphere which is over the land 
is more heated and rarefied than that which is over the sea. This 
occasions the wind to set in upon the land, as we find it regularly 
does on the coast of Guinea and other countries in the torrid zone. 
There are certain winds, called trade-w inds, the theory of which 
may be easily explained on the principle of rarefaction, affected, as 
it is, by the relative position of the different parts of the earth with 
the sun at different seasons of the year, and at various parts of the 
day. A knowledge of the laws by which these winds are controlled 
is of importance to the mariner. When the place of the sun with 
respect to the different positions of the earth at the different seasons 
of the year is understood, it will be seen that they all depend upon 
the same principle. The reason that the wind generally subsides 
at the going dowm of the sun is, that the rarefaction of the air, in 
the particular spot which produces the wind, diminishes as the sun 
declines, and, consequently, the force of the wind abates. The 
great variety of winds in the temperate zone is thus explained. 
The air is an exceedingly elastic fluid, yielding to the slightest 
pressure ; the agitations in it, therefore, caused by the regular 
winds, whose causes have been explained, must extend every way 
to a great distance, and the air, therefore, in all climates will suffer 
more or less perturbation, according to the situation of the country, 
the position of mountains, valleys, and'a variety of other causes 
Hence every climate must be liable to variable winds. The yuaiuy 
of winds is affected by the countries over which they pass: and 


172 * 


NATURAL PUJLOSOPEF. 


tiiey are sometimes rendered nestileutial bv the heat of deserts or 
the Dutrid exhalations of marshes and lakes. Thus, from the 
deserts of Africa, Arabia and the neighboring countries, a hot wind 
blows, called Samiel , or Simoon , which sometimes produces instant 
death. A similar wind blows from the desert of Sahara, upon the 
western coast of Africa, called the Harmaltan , producing a dryness 
and heat which is almost insupportable, scorching like the blasts 
of a furnace. 


How is wind 
sometimes af¬ 
fected by the 
face of a 
■ountry? 


622. Whirlwinds and Waterspouts. — The 
direction of winds is sometimes influenced by the 
form of lofty and precipitous mountains, which, 
resisting their direct course, causes them to 
descend with a spiral and whirling motion, and 


with great force. 


623. A similar effect is produced by two winds meeting at an 
angle, and then turning upon a centre. If a cloud happen to be 
between these two winds thus encountering each other, it will be 
condensed and rapidly turned round, and all light substances will 
be carried up into the air by the whirling motion thus produced. 


What is sup¬ 
posed to be the 
cause of water¬ 
spouts ? 


624. The whirlwind, occurring at sea, occa¬ 
sions the singular phenomenon of the water 
spout. 


Fig. 1U6. 














ACOUSTICS. 


175 


What does 
Fig. 105 rep¬ 
resent ? 


025. Fig. 105 represents the several forms in 
■which water-spouts are sometimes seen. 


626. From a dense cloud a cone descends in the form of a trumpet, 
with the small end downwards. At the same time, the surface of 
the sea under it is agitated and whirled round, the waters are con¬ 
verted into vapor, and ascend with a spiral motion, till they unite 
with the cone proceeding from the cloud. Frequently, however, 
they disperse before the junction is effected. Both columns diminish 
towards their point of contact, where they are sometimes not more 
than three or four feet in diameter. In the centre of the water¬ 
spout there is generally a vacant space, in which none of the small 
particles of water ascend. In this, as well as around the outer 
edges of the water-spout, large drops of rain fall. Water-spouts 
sometimes disperse suddenly, and sometimes continue to move 
rapidly over the surface of the sea, continuing sometimes in sight 
for the space of a quarter of an hour When the water-spout 
breaks, the water usually descends in the form of heavy rain. It is 
proper here to observe that by some authorities the phenomena of 
water-spouts are considered as due to electrical causes. 

627. A notion has prevailed that water-spouts are dangerous to 
shipping. It is true that small vessels incur a risk of being overset 
if they carry much sail, because sudden gusts of wind, from all 
points of the compass, are very common in the vicinity of water¬ 
spouts ; but large vessels, under but a small spread of canvas, 
encounter, as is said, but little danger. 

628. Pneumatics forms a branch of physical science which has 
been entirely created by modern discoveries. Galileo first demon¬ 
strated that air possesses weight. Ilis pupil, Torricelli, invented 
the barometer; and Pascal, by observing the difference of the alti¬ 
tudes of the mercurial column at the top and the foot of the Pay de 
Dome , proved that the suspension of the mercury is caused by the 
pressure of the atmosphere. Otto Guericke, a citizen of Magde¬ 
burg, invented the air-pump about the year 1654 ; and Boyle and 
Mariotte soon after detected, by its means, the principal mechanical 
properties of atmospheric air. Analogous properties have been 
proved to belong to all the other aeriform fluids. The problem of 
determining the velocity of their vibrations was solved by New'ton 
and Euler, but more completely by Lagrange. The theoretical prin¬ 
ciples relative to the pressure and motion of elastic fluids, from 
which the practical formulae are deduced, -were established by 
Daniel Bernoulli in his Hydrodynamica (1738), but have. bee& 
rendered more general by Navier. 

What ts 629. Acoustics. — Acoustics is the science 
Acousticst w hich treats of the nature and laws of sound. 

ft includes the theory of musical concord or harmony. 

15* 


NATURAL PHILOSOPHY. 


<74 


What L * 630. Sound is the sensation produced in the 
tound t organs of hearing by the vibrations or undulations 
transmitted through the air around.* 

631. If a bell be rung under an exhausted receiver, no sound can 
be heard from it; but when the air is admitted to surround the bell, 
the vibrations immediately produce sound. 

632. Again, if the experiments he made by enclosing the bell in 
a small receiver, full of air, and placing that under another receiver, 
from which the air can be withdrawn, though the bell, when struck, 
must then produce sound, as usual, yet it will not be heard if the 
outer receiver be well exhausted, and care be taken to prevent the 
vibrations from being communicated through any solid part of the 
apparatus, because there is no medium through which the vibrations 
of the bell in the smaller receiver can be communicated to the ear.f 

itti . , 633. Sounds are louder when the air sur- 

v\'hy is a sound 

louder in cold rounding the sonorous body is dense than when 
weather? ft j s j n a rarefied state, and in general the 

intensity of sound increases with the density of the medium 
by which it is propagated. 

634. For this reason the sound of a bell is louder in cold than 
in warm weather; and sound of any kind is transmitted tc a 
greater distance in cold, clear weather, than in a warm, sultry 
day. On the top of mountains, where the air is rare, the human 
voice can be heard only at the distance of a few rods; and the 
living of a gun produces a sound scarcely louder than the crack¬ 
ing of a whip. 

What are So- 635. Sonorous bodies are those which pro- 
norous bodies ? diice clear, distinct, regular, and durable 
30unds, such as a bell, a drum, wind instruments, musical 
strings and glasses. These vibrations can be communicated 
to a distance not only through the air, but also through 
liquids and solid bodies. 

* “ The seruation of sound is produced by the wave of air impinging on 
the membrane of the ear-drum, exactly as the momentum of a wave of the 
sea would strike the shore.” — [Lardner.] 

t In performing these experiments, the bell must be placed in such a man¬ 
ner that whatever supports it will rest on a soft cushion of wool, so as to 
prevent the vibrations from being communicated to the plate of the air 
pump, or any other of the solid parts of the apparatus. 


ACOUSTICS. 


m 


T It* what Jo 
bodies owe their 
sonorous prop¬ 
erties J 


636. Bodies owe their sonorous property 
to their elasticity. But, although it is un¬ 
doubtedly the case that all sonorous bodies arc 


elastic, it is not to be inferred that all elastic bodies are 


sonorous. 


637. The vibrations of a sonorous body give a tremulous or un 
dulatory motion to the air or the medium by which it is surrounded, 
similar to the motion communicated to smooth water when a stone 
is thrown into it. 


What are the 638. Sound is communicated more rapidly 
best conductors and with greater power through solid bodies 
oj sound ? than through the air, or fluids. It is conducted 
by water about four times quicker than by air, and by solids 
about twice as rapidly as by water. 


639. If a person lay his head on a long piece of timber, he can 
hear the scratch of a pen at the other end, wmle it could not be 
heard through the air. 

640. If the ear be placed against a long, dry brick wall, and a 
person strike it once with a hammer, the sound will be heard twice , 
because the wall will convey it with greater rapidity than the air, 
though each will bring it to the ear. 

641. It is on the principle of the greater power of solid bodies 
communicate sound that the instrument called the Stethoscope * is 
constructed. 

What is ttiT*\ 642. The Stethoscope is a perforated cylin- 
Stethoscope^ der, 0 f light, fine-grained wood, with a funnel- 
principle is it shaped extremity, which is applied externally to 
constructed? the' cavities of the body, to distinguish the 
sounds within. 


. . 643. By means of the stethoscope the phy- 

of the stetho - sician is enabled to form an opinion of the heal thy 

scope ? action of the lungs, and other organs to which the 

ear cannot be directly applied. 


* The word Stethoscope is derived from two Greek words, OTf&o$, the 
dreast, and ar.ontw , to examine, and is given to this instrument because 5 ‘. 
is applied to the breast of a person for the purpose of ascertaining the con- 
dition of the lungs and other internal organs. Dr. Webster suggests that 
the term Phonophorus, or Sound-conductor, would be a preferable name lc# 
the insu xmaut. 


176 


NATURAL PHILOSOPHY 


With what rapidity 644. Sound passing through the ai? 
does sound move / moves a t the rate of 1120 feet in a second 
of time; and this rule applies to all kinds of sound, whether 
loud or soft.* 

What kind of 645. The softest whisper, tnerefore, flies as fast 
sounds move as the loudest thunder; and the force and direction 
fastest ? 0 f the wind, although they affect the continuance 

of a sound, have but slight effect on its velocity. 

646. Were it not for this uniform velocity of all kinds of sound, 
the music of a choir, or of an orchestra, at a short distance, would 
he but a strange confusion of discordant sounds ; for the different 
instruments or voices, having different degrees of loudness, could not 
simultaneously reach the ear. 

647. The air is a better conductor of sound when it is humid than 
when it is dry. A bell can be more distinctly heard just before a 
rain ; and sound is heard better in the night than in the day, because 
the air is generally more damp in the night. 

648. The distance to which sound may be heard depends upon 
various circumstances, on which no definite calculations can be pre¬ 
dicated. Volcanoes, among the Andes, in South America, have been 
heard at the distance of three hundred miles ; naval engagements 
have been heard two hundred; and even the watchword “All ’s 
well,” pronounced by the unassisted human voice, has been heard 
from Old to New Gibraltar, a distance of twelve miles. It is said 
that the cannon fired at the battle of Waterloo were heard at Dover. 

649. A clear and frosty atmosphere is . favorable to the trans¬ 
mission of sound, especially where the surface over which it passes is 
smooth and level. Conversation in the polar regions has been carried 
on between persons more than a mile apart. The cannon in naval 
engagements in the English Channel have been heard in the centre 
of England. 

650. A blow struck under the water of the Lake of Geneva was 
heard across the whole breadth of the lake, a distance of nine miles. 
The earth itself is a good conductor of sound. The trampling of 
horses can be heard at a great distance by putting the ear to the 
ground, and the approach of railroad-cars can be ascertained when 
very far off by applying the ear to the rail. 

* The velocity of sound has sometimes been estimated as much a3 eleven 
hundred and forty-two feet in a second. The state of the air must, however, 
be taken into consideration. The higher the temperature, the greater the 
velocity; audit has been ascertained that within certain limits the velocity 
is increased about one foot for every degree that the thermometer rises. Ex¬ 
periments made with a cannon at midnight by Arago, Gay Lassac, and 
others, when the thermometer stood at GlP, gave 1118.39 feet per second as 
the velocity of sound. The rate stated in No. 644 will not therefore be fa? 
from the truth. The experiments which gave a result 4 eleven hundred and 
forty-two feet in a second were probably made when the weather was ex- 
t>eiuely warm 


A«?orSTJOS. 


177 


ro what prao- 6ol. J his umtorm velocity of sound enab es us 

tical use is the , , . .„ 

velocity of to ascertain i with some degree of accuracy, the 

sound appliedl distance of an object from which it proceeds. 


If, for instance, the flash of a gun at sea is seen a half of a minute 
before the report is heard, the vessel must be at the distance of about 
six miles. 

652. In the same manner the distance of a thunder-cloud may 
be estimated by counting the seconds that intervene between the 
flash of the lightning and the roaring of the thunder, and multiplying 
them by 1120. 

What is the ^' ITE Acoustic Paradox. —Sound, as has 

Arm,<ttir P n- a ^ rea % been stated, is propagated by the undulations 
dox? ° r of the air. Now, as these undulations or waves are 
precisely analogous to the case of two series of waves 
formed upon the surface of a liquid, there is a point where the 
elevation of a wave, produced by one cause, will coincide with the 
depression of another wave produced bji another cause, and the con¬ 
sequence will be neither elevation nor depression of the liquid. 


Explain the 654. When, therefore, two sounds are produced 
acoustic para - in different places, there is a point between them 
where the undulations will counteract each other, 
f.nd the two sounds may produce silence . 


655. A simple illustration of this fact may be made with a 
tuning-fork. If this instrument be put into vibration anddield up tc 
r.iie ear and rapidly turned, the sound, instead of being continuous, 
will appear to be pulsative or interrupted ; but, if slowly caused to 
revolve at a distance from the ear, a position of the forks will be 
found at which the sound will be inaudible. 

656. A similar experiment may be made with the tuning-fork 
held over a cylindrical glass vessel. Another glass vessel of sirailai 
kind being placed with its mouth at right angles to th.e first, no 
sound will be heard ; but, if either cylinder be removed, the sound 
will be distinctly audible in the other. The silence produced in this 
way is due to the interference of the undulations. 

This seeming paradox, when thus explained, like the paradox 
mentioned under the heads of Hydrostatics and Pneumatics, and 
another to be ment : oned under the head of Optics, will be found 
to be perfectly co* distent with the laws of sound. 

What is an 65T- An echo is produced by the vibrations 
echo ? 0 f t} ie a i r meeting a hard and regular surface, 

such as a wall, a ock, a mountain, and being reflected back 
to the ear, thus producing the same sound a second *»nU 
sometimes a third and fourth time 


i78 


NATUllA” PHILOSOPHY 


Why are there 
*w echoes at 
na, or on a 
vlain ? 

By u'hat law 
is sound re¬ 
flected ? 


658. For this reason, it is evl ent that no echo 
can be heard at sea, or on an extensive plain, where 
there are no objects to reflect the sound. 

659. Sound, as well as light and heat, is re¬ 
flected in obedience to the same law that has 
already been stated in Mechanics, namely, the 

angles of incidence and of reflection are always equal. 

660. It is only necessary, therefore, to know how sound strikes 
against a reflecting surface, to know how it will be reflected. It is 
related of Dionysius, the tyrant of Sicily, that he had a dungeon 
(called the ear of Dionysius) in which the roof was so constructed 
as to collect the words, and even the whispers, of the prisoners con¬ 
fined therein, and direct them along a hidden conductor to the place 
where he sat to listen ; and thus he became acquainted with the 
most secret expressions of his unhappy victims. 

On what 'principle 
are speaking-trum¬ 
pets constructed? 

662. The voice, instead of being diflused in the open air, is con¬ 
fined within the trumpet; and the vibrations which spread and fall 
against the sides of the instrument are reflected according to the 
angle of incidence, and fall in the direction of the vibrations, which, 
proceed straight forward. The whole of the vibrations are thus 
collected into a focus; and, if the ear be situated in or near that 
spot, the sound will be prodigiously increased. 

How is a hear- ®63. Hearing-trumpets, or the trumpets used 
ing trumpet by deaf persons, are also constructed on the same 
constructed? principle; but, as the voice enters the large end of 
the trumpet, instead of the small one, it is not so much confined, 
nor so much increased.* 


661. Speaking-trumpets are constructed 
on the principle of the reflection of sound. 


664. The musical instrument called the trumpet acts also on 
the same principle with the speaking-trumpet, so far as its form 
tends to increase the sound. 

665. The smooth and polished surface of the interior parts of 
certain kinds of shells, particularly if they be spiral or undulating. 


* In this connexion the author cannot refrain from giving publicity to the 
value of a pair of acoustic instruments worn by one of tho members of his 
family. They consist of two small hearing-trumpets of a peculiar construc¬ 
tion, connected by a slender spring with an adjusting slide, which, parsing 
over the head keeps both trumpets in their place. They are concealed 
from observation by the head-dress, and enable the wearer to join in con¬ 
versation of ordinary tone, from which without them she is wholly debarred. 
The inst.-uuicats were made by B. S. Codtnau & Co. 57 Tremout st., Boston. 


ACOUSTICS. 


17b 


fit thorn to collect ard reflect the various sounds which are taking 
place in the vicinity. Hence the Cyprias, the Nautilus, and some 
other shells, when held near the ear, give a continued sound, which 
resembles the roar of the distant ocean. 


On what prin - 666. Sound, like light, after it has been reflect- 
^whisperin'*- e< ^ ^ rom severa * surfaces may be collected into one 
galleries cot,- point, as a focus, where it will be more audible 
*tructed? than any other part; and on this principle 
whispering-galleries may be constructed. 


G67. The famous whispering-gallery in the dome of St. Paul's 
ehurch, in London, is constructed on this principle. Persons at 
rery remote parts of the building can carry on a conversation in a 
soft whisper, which will be distinctly audible to one another, while 
others in the building cannot hear it; and the ticking of a watch 
may be heard from side to side. 

668. There is a church in the town of Newburyport, in Massa 
chusetts, which, as was accidentally discovered, has the same prop¬ 
erty as a whispering-gallery. Persons in opposite comers of the 
building, by facing the wall, may carry on a conversation in the 
softest whisper, unnoticed by others in any other part of the build 
ing. It is the iDuilding which contains in its cemetery the remains 
of the distinguished preacher, Whitefield. 


What is an 689. Acoustic Tubes. — Sounds may be com 
Acoustic Tube 1 veyed to a much greater distance through contin¬ 
uous tubes than through the open air. The tubes used to con¬ 
vey sounds are called Acoustic Tubes. They are much used in 
public houses, stores, counting-rooms, &c., to convey communi¬ 
cations from one room to another. 


670. The quality of sound is affected by the furniture of a room, 
particularly the softer kinds, such as curtains, carpets, &c.; because, 
having little elasticity, they present surfaces unfavorable to vibra¬ 
tions. 

671. For this reason, music always sounds better in rooms with 
bare walls, without carpets, and without curtains. For the same 
reason, a crowded audience increases the difficulty of speaking. 

072. As a general rule, it may be stated that plane and smooth 
turfaces reflect sound without dispersing it; convex surfaces disperse it, 
md concave surfaces collect it. 


How is the 
found of the 
human voice 
!n educed * 


673. The sound of the human voice is pro¬ 
duced by the vibration of two delicate membranes 
situated at the top of the windpipe, between which 
the air from the lungs passes. 


180 


NATURAL PHILOSOPHY. 


074. The tones are varied from grave to acute, by tpenmg 01 
contracting the passage ; and they are regulated by the muscles 
belonging to the throat, by the tongue, and by the cheeks. The 
management of the voice depends much upon cultivation ; and 
although many persons can both speak and sing with ease, and with 
great power, without much attention to its culture, yet it is found 
that they who cultivate then* voices by use acquire a degree of flexi¬ 
bility and ease in its management, -which, in a great measure, sup¬ 
plies the deficiency of nature.* 

675. Ventriloquism t is the art of speaking ir. 
such a manner as to cause the voice to appear 
to proceed from a distance. 

676. The art of ventriloquism was not unknown to the ancients , 
and it is supposed by some authoru that the famous responses of the 
oracles at Delphi, at Ephesus, <fcc., were delivered by persons who 
possessed this faculty. There is no doubt that many apparently 
wonderful pieces of deception, which, in the days of superstition 
and ignorance, were considered as little short of miracles, were per¬ 
formed by means of ventriloquism. Thus houses have been made 

♦ Dr. Bush’s very valuable work on “ The Philosophy of the Human 
Voice,” contains much valuable matter in relation to the human voice 
Dr. Barber’s “ Grammar of Elocution,” and the “ Rhetorical Reader,” by 
the author of this volume, contain useful instructions in a practical form. 
To the work of Dr. Rush both of the latter works are largely indebted. 

f The word Ventriloquism literally means, “ speaking from the belly” and 
it is so defined in Chambers’ Dictionary of Arts and Sciences. The ven¬ 
triloquist, by a singular management of the voice, seems to have it in his 
power “ to throw his voice ” in any direction, so that the sound shall appear 
to proceed from that spot. The words are pronounced by the organs usu¬ 
ally employed for that purpose, but in such a manner as to give little or no 
motion to the lips, the organs chiefly concerned being those of the throat 
and tongue. The variety of sounds which the human voice is capable of 
thus producing is altogether beyond common belief, and, indeed,.is truly 
surprising. Adepts in this art will mimic the voices of all ages and condi¬ 
tions of human life, from the smallest infant to the tremulous voice of tot¬ 
tering age, and from the intoxicated foreign beggar to the high-bred, arti. 
ficial tones of the fashionable lady. Some will also imitate the warbling 
of the nightingale, the loud tones of the whip-poor-will, and the scream of 
the peacock, with equal truth and facility. Nor are these arts confined to 
professed imitators ; for in many villages boys may be found who are in 
the habit of imitating the brawling and spitting of cats in such a manner 
as to deceive almost every hearer. 

The human voice is also capable of imitating almost every inanimate 
sound. Thus, the turning and occasional creaking of a grindstone, with 
the rush of the water, the sawing of wood, the trundling and creaking 
of a wheelbxrrow, the drawing of corks, and the gurgling of the flow¬ 
ing liquor, the sound of air rushing through a crevice on a wintry night 
and a great variety of other noises of the same kind, are imitated by the 
voice so exactly as to deceive any hearer who does not know whence thej 
proceed. 


What is Ven¬ 
triloquism, ? 


ACOUSTICS. 


181 


to appear haunted, voices have been heard from toml.s, and the iead 
have been made to appear to speak, to the great dismay of the 
neighborhood, by means of this wonderful art. 

Ventriloquism is, without doubt, in great measure the gift oi 
nature ; but many persons can, with a little practice, utter sounds 
and pronounce words without opening the lips or moving the mus> 
cles of the face; and this appears to be the great secret of the 
art. 


tt • ,, 677. Musical Sounds, or Harmony. — The 

How ts the . . . 

sound of a mu- sound produced by a musical string is caused by 
sical string its vibrations; and the height or depth of the 
tone depends upon the rapidity of these vibra¬ 
tions. Long strings vibrate with less rapidity than short ones; 
and for this reason the low tones in a musical instrument pro¬ 
ceed from the long strings, and the high tones from the short 


ones. 


Explain 
Fig. 106. 


Fig. 106. A B represents a musical string, 

Fig. 106. 

—G--., 

^__ 1 .,_____ - -- ~~ > V N 


678. 

If it be 
drawn 
up to G, its elas¬ 
ticity will not on- A -—— -—- — 

.y carry it back 
again, but will 
give it a momen¬ 
tum which will carry it to H, from whence it will successively 
return to T, F, C, D, &c., until the resistance of the air entirely 


--- 

"" -if -"" 


destroys its motion. 

. 7 , , 679. The quality of the sound produced by 

the quality of strings depends upon their length, thickness, 
the tone of a we ight, and degree of tension. The quality 
strmg depend? ^ the sound produced by wind ’nstruments 

depends upon their size, their length, and their internal diame¬ 


ter. 

680. When music is made by the use of strings, the air is struck 
by the body, and the sound is caused by the vibrations ; when it is 
made by pipes, the body is struck by the air; but, as action and re¬ 
action are equal, the effect is the same iD both cases. 

681. Long and large strings, when loose, produco the lowest 

16 




NATURAL PHILOSOPHY. 


182 


tones ; but different tones may be produced from the same string, 
according to the degree of tension. Large wind instruments, also, 
produce the lowest tones; but different tones may be produced 
from the same instrument, according to the distance of the aperture 
for the escape of the wind from the aperture where it enters. 

H°w does the 682. The qu dity of the sound of all musical 
temperature of , . 

the weather af- instruments is affected by the changes in the 

feet the tone of temperature and specific gravity of the atmos- 
a musical in¬ 
strument l 


683. As heat expands and cold contracts the materials of which 
the instrument is made, it follows that the strings will have a 
greater degree of tension, and that pipes and other wind instru¬ 
ments will be contracted, or shortened, in cold weather For this 
reason, most musical instruments are higher in tone (or sharper) 
in cold weather, and lower in tone (or more flat) in warm weather 


On what is the 
science of har¬ 
mony founded? 


684. The science of harmony is founded on 
the relation which the vibrations of sonorous 
bodies have to each other. 


685. Thus, when the vibrations of one string are double those ot 
another, the chord of an octave is produced. If the vibrations of 
two strings be as two to three, the chord of a fifth is produced. 
When the vibrations of two strings frequently coincide, they pro¬ 
duce a musical chord ; and when the coincidence of the vibrations 
is unfrequent, discord is produced. 

686. A simple instrument, called a monochord, contrived for the 
purpose of showing the length and degree of tension of a string to 
produce the various musical tones, and to show their relations, may 
thus be made. A single string of catgut or wire, attached at one 
end to a fixed point, is carried over a pulley, and a weight is sus¬ 
pended to the other end of the string. The string rests on two 
bridges, between the fixed point and the pulley, one of which is 
fixed, the other movable. A scale is placed beneath the string by 
which the length of the vibrating part between the two bridges 
may be measured. By means of this simple instrument, the respect¬ 
ive lengths required to produce the seven successive notes of the 
gamut will be as follows : it being premised that the longer the 
string the slower will be its vibrations. 

687. Let the length of the string required to produce the note 
called C be X ; the length of the string to produce the successive 
notes will be 


CDEFGA B C 
1 8 4322 8 1 

J 3 E» ? 2 5 TT 2 ' 


ACOUSTICS. 


$88. Konce, the octave will require 
jw <7 half of the length of the fundamen¬ 
ts note, and the vibrations that produce 
it »<dll be as two to one. The vibrations 
of She string in producing the successive 
notes of the scale will be as follows: 

CD.EFQA B C 

1 t I I § S V- 2. 

That is, to produce the note D nine vibra¬ 
tions will be made in the same time that 
eight are made by C, five of E to four of 
C, four of F to three of C, three of G 
to two of C, five of A to three of C, 
fifteen of B to eight of C, and two of 
the octave C to one ol the fundamen¬ 
tal C. 

689. The same relations exist in each 
successive octave throughout the whole 
nusical scale. 

690. As harmony depends upon the 
coincidence of vibrations, it follows that 
the octave produces the most perfect har¬ 
mony ; next in order is the fifth, as 
every third vibration of the fifth corre¬ 
sponds with every second vibration of the 
fundamental. Next to the fifth in the 
order of harmony follows the fourth, and 
after the fourth the third. 

691. The following scale, containing 
three octaves, exhibits the proportions 
which exist between the fundamental and 
all the other notes within that compass. 

692. In the lowest line of this scale 
the numbers show the intervals. The 
figures above express the number of 
’ibrations of the fundamental or tonic, 
and the upper line of figures represents 
the proportionate vibrations of each suc¬ 
cessive interval. 

693. It is found in practice that when 
two sounds are caused by vibrations 
which are in some simple numerical pro- 
nortion to each other, such as 1 to 2, or 
2 to 3, or 3 to 4, &c., they are pleasing 
to the ear ; and the whole science of har¬ 
mony is founded on such relations. 

694. The principal harmonies are the 
nctave, fifth, fourth, major third, and 






































































184 


NATURAL PHILOSOPHY. 


minor third ; and the relations between them and the fundamental 
or tonic are as follows ; 

Octave, 2 to 1. 

Fifth, 3 “ 2. 

Fourth, 4 “ 3. 

Major Third, 5 “4. 

Minor Third, 6 “ 5. 

695. The following Rules may serve as the basis of interesting 
calculations. 

(1.) Strings of the same diameter and equal tension vibrate iu 
times in an inverse proportion to their lengths. 

(2.) The vibrations of strings of equal length and tension are in 
an inverse proportion to their diameters. 

(3.) The vibrations of strings of the same length and diameter 
are as the square roots of the weights causing their tension. 

(4.) The vibrations of cylindric tubes closed at one end are in an 
inverse proportion to their length. , 

(5.) The sound of tubes open at both ends is the same with that 
of tubes of half the length closed at one end. 

[The limits of this work will not admit the further consideration 
of the subject of Harmony. It constitutes of itself a science, in¬ 
volving principles which require deep study and investigation ; and 
they who would pursue it advantageously will scarcely expect, in 
the pages of an elementary work of this kind, that their wants will 
be supplied.] 


696. Questions for Solution. 

(1.) A rocket was seen to explode, and in two seconds the sound of the 
explosion was heard ; how far off was the rocket 1 Ans. 2240 ft. 

(‘2.) The flash from a cloud was seen, and in live seconds the thunder was 
heard ; what was the distance of the cloud 1 A ns. 5600. ft. 

(3.) A musical string four feet long gave a certain tone; what must be 
the length of a string of similar size and tension to produce the note of a 
fifth 1 A ns. 2 ft. 8 in. 

(4.) A certain string vibrates 100 times in a second ; how many times 
must a string of the same kind vibrate to produce the octave 1 the fifth 1 
the minor third 1 the major third 1 Ann. 2uu; 150; 120; 125. 

(5.) Supposing that two sounds, with all their attending circumstances 
similar, reach an ear situated at the point of interference of the undula¬ 
tions, — what will be the consequence 1 [See Nos. 653 and 654.] 

(6.) The length of a string being 36, what will be length of its octave '1 
fifth 1 fourth 1 major and minor thirds 1 Ans. IS; 24; 27; 28.8; 80. 

(7.) A stone, being dropped into a pit, is heard to strike the bottom in 
7 seconds ; how deep was the pit 1 Ans. Bj r Algebra, 600 ft. 

[N. B. In estimating the velocity of sound, it is generally reckoned iq 
practice as only at 1090 feet per second, supposing the thermometer at the 
freezing point ; and one foot per second is added for every degree of tern 
perature above the freezing point, or 32°. The average rate of 1120 feel 
has been assumed in the text,.] 


PYRONOMICS. 


ISo 


(8.) Suppose tlie length of a music-string to le five feet; what will ho 
the length of the loth, all'other circumstances being equal 1 Ans. 4 in. 

(9.) The length of the fifth being four, what will be the length of the 
fundamental, or tonic 1 Ans. 6, 

(10.) What must be the length of a pipe of an open diapason to produoe 
the same tone with four foot C of the stopped diapason 1 Ans. 4ft. 

[N. B. The open diapason consists of pipes open at both ends ; the 
stopped diapason has it3 pipes closed at one end. [See No. 695 (5).J 

(11.) In what proportion are the vibrations of two strings of equal 
length and diameter, one stretched with a weight of twenty-five pounds, 
the other with a weight of fifty pounds 1 \See No. 695 (8).] Ans. 1 to 1.41 + 
(12.) In what proportion are the vibrations of two strings of equal 
length and tension, but having diameters in the proportion of i to 5 1 

Ans. 5 to 8. 

What is Py- 697. PYRONOMICS, OR THE LAWS OF 
ronomics ? Heat. — Pyronomics is the science which 

treats of the laws, the properties and operations of heat. 

What is heat , 698. nature of heat is unknown, but it 

and what is its has been proved that the addition of heat to any 
weight ? substance produces no perceptible alteration in 

the weight of that substance. Hence it is inferred that heat is 
imponderable. 

699. Heat is undoubtedly a positive substance, 
What is cold? or quality. Cold is merely negative, being only 
the absence of heat. 


What effect 700. ^ eat pervades all bodies, insinuating 
has heat on all itself, more or less, between their particles, 
bodies? and forcing them asunder. Heat and the 

attraction of cohesion constantly act in opposition to each 
other; hence, the more a body is heated, the more its par¬ 
ticles will be separated. 


701. Heat causes most substances to dilate or expand, while 
cold (which is merely the absence of heat) causes them to contract.* 
Since there is a continual change in the temperature of all bodies 
on the surface of the earth, it necessarily follows that there will be 
a constant corresponding change in their magnitude as they are 
affected by heat and cold. They expand their bulk in a warm day, 
and contract it in a cold one. In warm weather the flesh swells, 


* The exceptions to this remark are water and day. 
it freezes ; clay contracts when heated. 

16* 


Water expands wheu 


HJKAL PHILOSOPHY. 


L86 


the blood-vessels are well filled, the hands and the feet, as Will as 
bthei parts of the body, expand or acquire a degree of plumpness 
and the skin is distended ; while, on the contrary, in cold weather 
the flesh appears to contract, the vessels shrink, and the skin 
appears shrivelled. Hence a glove or a shoe which is too. tight in 
the summer will often be found to be easy in cold weather. 

702. The effect of heat in separating the particles of different 
kinds of substances is seen in the melting of solids, such as metals, 
wax, butter, &c. The heat insinuates itself between the particles, 
and forces them asunder. These particles then are removed from 
that degree of proximity to each other within which cohesive attrae 
tion exists, and the body is reduced to a fluid form. When th 
heat is removed the bodies return to their former solid state. 


What kind of 
bodies arrest 
the progress 
of heat ? 

What is 
steam ? 


703. Heat passes through some bodies with 
more difficulty than through others, but there is 
no kind of matter which can completely arrest its 
progress. 

704. Of all the effects of heat, that produced upon 
water is, perhaps, the most familiar. The particles 
are totally separated, and converted into steam or vapor, and 
their extension is wonderfully increased. The steam wb ; ch 
arises from boiling water is nothing more than portions of the 
water heated. The heat insinuates itself between the par¬ 
ticles of the water, and forces them asunder. When deprived 
of the heat, the particles will unite in the form of drops of 
water. 

This fact can be seen by holding a cold plate over boiling water. 
The steam rising from the water will be condensed into drops on 
the bottom of the plate. The air which we breathe generally con 
tains a considerable portion of moisture. On a cold day this 
moisture condenses on the glass in the windows, and becomes 
visible. We see it also collected into drops on the outside of a 
tumbler or other vessel containing cold water in warm weather. 
Heat aloo produces most remarkable effects upon air, causing it to 
expand to a wonderful extent, while the absence of heat causes it 
to shrink or contract into very small dimensions. 


How is rain 
produced? 


water. 


705. The attraction of cohesion causes the 
small watery particles which compose mist or 
vapor to unite together in the form of dreps of 
It is thus that rain is produced. The clouds ctwst <jf 


PYllOJNOMIOS. 


1S7 


mist or vapor expanded by heat. They rise to the cold regions 
of the skies, where the particles of vapor lose their heat, and 
then, uniting in drops, fall to the earth. But so long as they 
retain their heat the attraction of cohesion can have no influence 
upon them and they will continue to exist in the form of steam, 
vapor or mist. 

706. The thermometer, an instrument designed to measure degrees 
of heat, has already been described, in connexion with the barom¬ 
eter, under the head of Pneumatics. Heat, under the name of 
caloric, is properly a subject of consideration in the science of 
Chemistry. It exists in two states, called, respectively, free heat 
and latent heat. Free heat, or free caloric, is that which is per¬ 
ceptible to the senses, as the heat of a fire, the heat of the sun, &c. 
Latent heat is that which exists in most kinds of substances, but is 
not perceptible to the senses until it is brought out by mechanical 
or chemical action. Thus, when a piece of cold iron is hammered 
upon an anvil, it becomes intensely heated ; and when a small 
portion of sulphuric acid, or vitriol, is poured into a vial of cold 
water, the vial and the liquid immediately become hot. A further 
illustration of the existence of latent or concealed heat is given at 
the fireside every day. A portion of cold fuel is placed upon the 
grate or hearth, and a spark is applied to kindle the fire which 
warms us. It is evident that the heat given out by the fuel, when 
ignited, does not all proceed from the spark, noi can we perceive it 
in the fuel ; it must, therefore, have existed somewhere in a latent 
state. It is, however, the effects of free heat, or free caloric, which 
are embraced in the science of Pyronomics. The subject of latent 
heat belongs more properly to the science of Chemistry. 

707. The terms heat and cold, as they are generally used, are 
merely relative terms ; for a substance which in one person would 
excite the sensation of heat might, at the same time, seem cold to 
another. Thus, also, to the same individual the same thing may be 
made to appear, relatively, both warm and cold. If, for instance, a 
person were to hold one hand near to a warm fire, and the other on 
a cold stone, or marble slab, and then plunge both into a basin of 
lukewarm water, the liquid would appear cold to the warm hand 
and warm to the cold one. 


708. Sources of Heat.— The four prin¬ 
cipal sources of the development of heat are 
the Sun, Electricity, Chemical Action and Me¬ 
chanical Action. The heat produced by fire 
a-id flame is due to chemical action. 


What are the 
principal, 
soured of 
heat ? 


NATURAL PlIILOSuPHY. 


188 


7 709. But, of all the sources from which heat 

What is the 

source of the has been developed by human agency, that pro- 
grcatest degree duced by electrical action, and especially tho 
galvanic battery, is by far the most eminent is 
its degree and in its effects. It can reduce the most refractory 
substances to a fluid state, or convert them to their origina 
elements. 


710. The heat generally ascribed to the sun is attended by 
peculiar phenomena, but imperfectly understood. It may, perhaps, 
be questioned whether there be any absolute heat in the rays of 
that luminary, for we find that the heat is not in all cases propor¬ 
tionate to his proximity. Thus, on the tops of high mountains, 
and at great elevation, it is not found that the heat is increased, 
but, on the contrary, diminished. But there are other phenomena 
which lead to the conclusion that his rays are accompanied by the 
development of heat, if they are not-the cause and the source of it. 

711. All mechanical operations are attended by heat. Friction, 
sudden compression, violent extension, are all attended by heat. 
The savage makes his fire by the friction of two pieces of dry wood. 
Air, suddenly and violently compressed, ignites dry substances ; * 
and India-rubber especially, when suddenly extended, shows evident 
signs of heat; and an iron bar may be made red hot by beaming it 
quickly on an anvil. Even water, when strongly compressed, gives 
out heat. 


What are the Tlie P rinci P al effects of heat are 

principal ef- three, namely : 

fxts oj heat ? (1.) Heat expands most substances. 

(2.) It converts them from a solid to a fluid state. 

(3.) It destroys their texture by combustion. 


713. There are many substances on which ordinary degiees of 
heat, and, indeed, heat of great intensity, seems to produce no 
sensible effects ; and they have, therefore, received the name of 
incombustible bodies. Bodies usually called incombustible are 
generally mineral substances, such as stones, the earths, &c. All 
vegetable substances, and piost animal substances, are highly com¬ 
bustible. The metals also all yield to the electrical or galvanic 
battery. But there is sufficient evidence that all bodies were once 
in a fluid or gaseous state, and that the solid forms that they have 
assumed are due to the loss of heat. Could the same degree of 


* Syringes have been constructed on this principle A solid pistoa 
being forcibly driven downward on dry tinder, ignites it 


PYKONOMICS. ISO 


h,% osity of heat he restored, it is presumed that they would resume 
their liquid or gaseous form. 


- Whtti is the 
first law of 
heat l 


714. Heat tends to diffuse itself equally through 
all substances. 


If a heated body be placed near a cold one, the temperature of 
the former will be lowered, while that of the latter will be raised. 
All substances contain a certain quantity of heat; but, on account 
of its tendency to diffuse itself equally, and the difference in the 
power of different substances to conduct it, bodies of the same 
absolute temperature appear to possess different degrees of heat. 

Thus, if the hand be successively applied to a woollen garment, a 
mahogany table, and a marble slab, all of which have been for some 
time in the same room, the woollen garment will appear the warmest, 
and the marble slab the coldest, of the three articles ; but, if a ther¬ 
mometer be applied to each, no difference in the temperature will 
be observed. 


What is the 
reason that 
some sub¬ 
stances feel 
warm and 
others cold in 
the same room? 

hand; while 
heat, receives 
imperceptible, 

What is the 
cause of the 
difference in 
the warmth of 
different gar¬ 
ments ? 


715. From this it appears that some substances 
conduct heat readily , and others with great dif¬ 
ficulty. The reason that the marble slab seems 
the coldest is, that marble, being a good con¬ 
ductor of heat, receives the heat from the hand 
so readily that the loss is instantly felt by the 

the woollen garment, being a bad conductor of 
the heat from the hand so slowly that the loss is 

716. The different power of receiving and 
conducting heat, possessed by different substances, 
is the cause of the difference in the warmth of 
various substances used for clothing. 


Why are 717. Thus, woollen garments are warm gar- 

woollen gar- raents, because they part slowly with the heat 

meats warm , w hich they acquire from the body, and, conse- 
znd linen, cool? . (1 . , ,, . 

quently, they do not readily convey the warmth 

of the body to the air; while, on the contrary, a linen garment 
is a cool one, because it parts with its heat readily, and as read* 
ily receives fresh heat from the body. It is, therefore, con¬ 
stantly receiving heat from the body and throwhig it out into 


190 


NATURAL PHILOSOPHY. 


the ai/ while the woollen garment retains the heat which it 
receive^, and thus encases the body with a warm covering. 

718. For a similar reason, ice in summer is wrapped in woollen 
cloths. It is then protected from the heat of the air, and will not 
melt. 

How is heat 719. Heat is propagated in two ways, namely, 
‘propagated? ^ con( j uc ^ on anc [ by radiation. Heat is propa¬ 
gated by conduction when it passes from one substance to 
an jther in contact with it. Heat is propagated by radiation 
when it passes through the air, or any other elastic fluid. 

720. Different bodies conduct heat with differ- 
What are the en t degrees of facility. The metals are the best 
^ors' of°heat*~ con ductors; and with regard to their conducting 
power, stand in the following order, namely: Gold, 
platinum, silver, copper, iron, zinc, tin, lead. 

721. Any liquid, therefore, may be more readily heated in a 
silver vessel than in any other of the same thickness, except one oi 
gold, or of platinum, on account of its great conducting power. 

Why are the 722. Metals, on account of their conducting 
handles of tea power, cannot be handled when raised to a tempe- 
< made'qfwoodt rature above 120 degrees of Fahrenheit. For this 
reason, the handles of metal tea-pots and coffee¬ 
pots are commonly made of wood; since, if they were made of 
metal, they would become too hot to be grasped by the hand, 
soon after the vessel is filled with heated fluid. 

723. Wood conducts heat very imperfectly. For this reason, 
wooden spoons and forks are preferred for ice. Indeed, so imper¬ 
fect a conductor of heat is wood, that a stick of wood may be grasped 
by the hand while one end of the stick is a burning coal. But an 
iron bar, being a good conductor of heat, cannot be handled near 
the heated end. 

724. Animal and vegetable substances, of a loose texture, such 
as fur, wool, cotton, &c., conduct heat very imperfectly, hence their 
efficacy in preserving the warmth of the body. Water becomes 
scalding hot at 150 degrees; but air, heated far beyond the tempe¬ 
rature of boiling water, may be applied to the skin without much 
pain. Sir Joseph Banks, with several other gentlemen, remained 
some time in a room when the heat was 52 degrees above the boiling 
point; but, though they could bear the contact of the heated air 
they could not touch any metallic substance, as their watch-chains 


PYUONOMIOS. 


l'Ji 


cione) &c. Eggs, placed on a tin frame, were roastel hard in 
twenty minutes ; and a beef-steak was overdone in thirty-three 
minutes. 

725. Chantrey, the celebrated sculptor, had an oven which ne 
used for drying his plaster cuts and moulds. The thermometer gen¬ 
erally stood at 300 degrees in it, yet the workmen entered, and 
remained in it some minutes without difficulty ; but a gentleman 
once entering it with a pair of silver-mounted spectacles on, had his 
face burnt where the metal came in contact with the skin. 

726. The air, being a bad conductor, never radiates heat, nor is 
it ever made hot by the direct rays of the sun The air which comes 
in contact with the surface of the earth ascends, and warms the air 
through which it passes in its ascent. Other air, heated in the 
same way, also ascends, carrying heat, and this process is repeated 
till all the air is made hot. 

727. In like manner, in cold weather, the air resting on the earth 
is made cold by contact. This cold air makes the air above it cold, 
and cold currents (or wind) agitate the mass together till a uniform 
temperature is produced. 

__ . . 728. Heat is reflected by bright substances, and 

How is heat . . ® ’ 

reflected? the an g Ie oi reflection will be equal to the angle 

of incidence. 


729. Advantage has been taken of this property of heat in the 

construction of a simple apparatus for baking. It is a bright tin 
case, having a cover inclined towards the fire in such a manner as 
to reflect the heat downwards. In this manner use is made both of 
the direct heat of the fire, and the reflected heat, which would other¬ 
wise pass into the room. The whole apparatus, thus connected with 
the culinary department, is called, in New England, “ The Connect¬ 
icut baker.” 0 

730. This power of reflecting heat, possessed by bright sub¬ 
stances, is the reason why andirons and other articles that are kept 
bright, although standing very near the fire, never become hot; 
while other darker substances, further from the fire, become hot. 
But, if they are not bright, heat will penetrate them. 

731. The reflecting power of bright and light colored substances 
accounts also for the superior coolness of whiue and light-colored 
fabrics for clothing. 


Why are dark 
garments 
warmer than 
hght ones? 


732. Black and dark-coloied surfaces absorb 
heat. This is the reason why black and dark- 
colored fabrics are warmer when made into gar¬ 
ments than those of light color. 


733. Snow or ice will melt under a piece of black cloth, while 
It would remain perfectly solid under a white one. The farmers ir? 
Boino of the mountainous parts of Europe are accustomed to spread 


192 


NATUKAL PHILOSOPHY. 


black earth, or soot, over the snow, in the spring, to hasten its 
melting, and enable them to commence ploughing. 

Whut effect has heat 734 The density of all substances is aug- 

substances? mented by cold, and diminished by heat. 

There is a remarkable exception to this remark, and that is in the 
case of water ; which, instead of contracting, expands at the freez¬ 
ing point, or when it is frozen. This is the reason why pitchers, 
and other vessels, containing water and other similar fluids, are so 
often broken when the liquid freezes in them. For the same reason, 
ice floats instead of sinking in water ; for, as its density is dimin¬ 
ished, its specific gravity is consequently diminished. Were it not for 
this remarkable property of water, large ponds and lakes, expose^ 
to intense cold, would become solid masses of ice; for. if the ice, 
when formed on the surface, were more dense (that is, more heavi) 
than the water below, it would sink to the bottom, and the water 
above, freezing in its turn, would also sink, until the whole body 
of the water would be frozen. The .consequence would be the total 
destruction of all creatures in the water. But the specific gravity 
of ice causes it to continue on the surface, protecting the water 
below from congelation. 


What is 
cold? 


735. Cold is merely the absence of heat; or rather, 
more properly speaking, inferior degrees of heat are 
termed cold. 


736. The effect of heat and cold, in the expansion and contrac 
tion of glass, is an object of common observation ; for it is this 
expansion and contraction which cause so many accidents with glass 
articles. Thus, when hot water is suddenly poured into a cold glass 
of any form, the glass, if it have any thickness, will crack ; ana 
on the contrary, if cold water be poured into a heated glass vessel 
the same effect will be produced. The reason of which is this ; 
Heat makes its way but slowly through glass ; the inner surface, 
therefore, when the hot water is poured into it, becomes heated, 
and, of course, distended before the outer surface, and the irregular 
expansion causes the vessel to break. There is less danger of frac¬ 
ture, therefore, when the glass is thin, because the heat readily pen¬ 
etrates it, and there is no irregular expansion. 

737. The glass chimneys, used for oil and gas burners, are often 
broken by being suddenly placed, when cold, over a hot flame. The 
danger of fracture may be prevented (it is said) by making a mi¬ 
nute notch on the bottom of the tube with a diamond. This precau¬ 
tion has been used in an establishment where six lamps were lighted 
every day, and not a single glass has been broken in nine years 

What bodies retain 738. Different bodies require different quan- 
huit Jie longest titles of heat to raise them to the same tern 


PYKONOMICS. 


perature; and those which are heated with most difficulty retain 
their heat the longest. 

Thus, oil becomes heated more speedily than water, and it 
likewise cools more quickly. 

739. The most obvious and direct effect of heat on a body 

! is to increase its extension in all directions. 

740. Coopers, wheelwrights and other artificers, avail themselves 
of this property in fixing iron hoops on casks, and the tires or irons 
on wheels. The hoop or tire, having been heated, expands, and, 
being adapted in that state to the cask or the wheel, as the metal 
contracts in cooling it clasps the parts very firmly together. 

741. From what has been stated above, it will be seen that an 
allowance should be made for the alteration of the dimensions in 
metallic beams or supporters, caused by the dilatation and contraction 
effected by the weather. In the iron arches of Southwark Bridge, 
over the Thames, the variation of the temperature of the air causes 
a difference of height, at different times, amounting to nearly an inch. 

A happy application of the expansive power of heat to the mechanic 
arts was made some years ago, at Paris. The weight of the roof of a 
building, in the Conservatory of Arts and Trades, had pressed out¬ 
wards the side walls of the structure, and endangered its security 
The following method was adopted to restore the perpendicular 
direction of the structure. Several apertures were made in the 
- walls, opposite to each other, through which iron bars were intro¬ 
duced, which, stretching across the building, extended beyond the 
outside of the walls. These bars terminated in screws, at each end, 
to which large broad nuts were attached. Each alternate bar was 
then heated by means of powerful lamps, and their lengths being thus 
increased, the nuts on the outside of the building were screwed up 
close to it, and the bars were suffered to cool. The powerful con¬ 
traction of the bars drew the walls of v the’building closer together 
and the same process being repeated on ail the bars, the walls were 
gradually and steadily restored to their upright position. 


742. The Pyrometer is an instrument to 
show the expansion of bodies by the applica¬ 
tion of heat. 


What is the 
Pyrometer' ? 


it consists of a metallic bar or w re, with an index connected 
with one extremity. On the application of heat, tho bar expands, 
and turns the index to show the degree of expansion. 

743. Wedgewood’s pyrometer, the instrument commonly 
used foi high temperatures, measures heat by the contraction of 



17 



1*J4 


NATURAL PHILOSOPHY. 


What effect 744 The expansion caused by heat ta 
Aas heat on solid and liquid bodies differs in different sub- 
^eiy ^n^the stances 5 aeriform fluids all expand alike, 

solid, liquid and and undergo uniform degrees of expansion at 
aeriform state ? 

J various temperatures. 

715. The expansion of solid bodies depends, in some degree, on 
the cohesion of their particles ; but, as gases and vapors are desti 
fcute of cohesion, heat operates on them without any opposing power. 

746. When heat is applied to water or other 
What effect liquids, it converts them into steam or vapor. The 
the form 1 of deprivation of heat reconverts them into the liquid 
liquid bodies ? form. It is on this principle that distillation takes 
place. 

What is a 747. The vessel employed for distillation is called 
’ a Still.* 

Fig. 10?. 



Explain 748. Fig. 107 represents a Still. A liquid being poumi 
Fig. 107. * nt0 ] ar g e vesse i heat i s applied below, which 
converts the liquid graduall y into steam or vapor, which, having 
no other outlet, passes through the spiral tube, called the worm, 
in vessel b f and from b through another worm, in c. The worm, 
being surrounded- with cold water, condenses the vapor in the 
tube or worm, and reconverts it to a fluid state, and it flows out 

* The subject of distillation properly belongs to the science of Chemistry, 
but it ia here introduced for the benefit of those who cannot realily 
U; u treatise on that subject 













I’YJRONOMICS. 


1115 


U e in a tepid stream. The worm is of different lengths, and its 
only use is to present a large extent of surface to the cold water, 
so that the vapor may readily be condensed. 

749. The process of distillation is sometimes used to purify a 
liquid, as the vapors which rise are unmixed with the impurities of 
the fluid. Important changes are thus made, and the still becomes 
highly useful in the arts. 


At what tem- 750. When water is raised to the tempera- 
wateT- 1 convert- ture Fahrenheit’s thermometer, it 

ed into steam ? is converted into steam. It is then highly 
elastic and compressible. 

What effect 751. The elastic force of steam is increased 
has heat upon by heat; and decrease of heat diminishes it. 

The amount of pressure which steam will exert 
depends, therefore, on its temperature. 

___ . , 752. The temperature of steam is always the 

temperature same with that of the liquid from which it is 
of confined formed, while it remains in contact with that liquid , 
steam . and w k en h ea q e d to a great degree, its elastic force 

will cause the vessel in which it is contained to burst, unless it 
is made sufficiently strong to resist a prodigious pressure. 

753. It has already been stated that water is converted into 
steam at the temperature of 212°. When closely confined it may be 
raised to a higher temperature, and it will then emit steam of 
greatly increased elastic force. 

How is steam 754 . When any portion of steam comes in 
condensed? contact with water, it instantly parts with its 
heat to the water, and becomes condensed into water. The 
whole mass then becomes water, increased in temperature 
by the amount of heat which the steam has lost. 

On what prop- 755. This is the great and peculiar property 

erty do the 0 f steam, on which its mechanical agencies de- 
mechanical , , - 7 . . 

agencies of pend, namely, its power of exerting a high 

steam depena ? degree of elastic force , and losing it hist an 

taneously. 


196 


NATURAL PHILOSOPHY. 


How matin « 756. There are two ways in which steam 

v&chanical } g made instantly to lose its mechanical force ; 
be instantly namely, first , by suddenly opening a passage 
destroyed ? f or its escape into the open air, where it imme¬ 
diately becomes visible,* by a sudden loss of part of its heat, 
which it gives to the air; and secondly , by conveying it to 
% vessel called a condenser, where it comes directly into 
contact with a stream of water, to which it instantly gives 
up its heat and is condensed into water. 

What space 757. Steam occupies a space about seven- 
does t!*am oc- teen hundred times larger than when it is con- 
ru Py verted into water. But the space that a given 

quantity of w T ater converted into steam will occupy depends 
upon the temperature of the steam. The more it is heated 
the greater space it will fill, and the greater will be its 
expaivsive force. -SL 

What is the 758. The Steam-engine. — The Steam- 
Steam-engine ? en gi ne j 3 a machine moved by the expansive 

force of steam. 

In ivhat man- 759. The mode in which steam is made to act 
ner is steam is by causing its expansive force to raise a solid 
made to act ? piston accurately fitted to the bore of a cylinder, 
like that in the forcing-pump. The piston rises by the impulse 
of expanding steam, admitted into the cylinder below. When 
the piston is thus raised, if the steam below it be suddenly con¬ 
densed by the admission of cold water, or withdrawn from under 


* Steam in a highly elastic state — that is, when at a high temperature — 
Is perfectly dry and invisible. The reason that we are able to see it after it 
has performed its work and issues from the steam-engine is, that as soon as it 
comes in contact with the air it immediately parts with a portion of its 
heat (and, because air is not a good conductor, only a portion), and is con 
densed into small vesicles, which present a visible form, resembling smoke 
Its expansive force, however, is not wholly destroyed; for the vesicles them 
selves expand as they rise, and soon become invisible, mingling with other 
vapois in the air. Could we look into the cylinder, filled with highly elastic 
steam, we should be able to see nothing. Rut, that the steam is there, and 
ir. its invisible form exerting a prodigious force, we know by the moiemeuts 
of the piston 


STEa M-ENGINE. 


19 ? 


it, a vacuum wiL be .formed, and the pressure of the atmosphere 
on the piston above will drive it down. The admission of more 
steam below will raise it again, and thus a continued motion 
of the piston, up and down, will be produced. This motion nf 
the piston is communicated to wheels, levers, and other machinery, 
in such a manner as to produce the effect intended. * 

How was the 760. This is the mode in which the engine of 
stcam-engine AT . 0 , ,, , 

0/Newcomen ^ ewcomen and bavery, commonly called the at- 

j?id Savery mospheric engine, was constructed. It was called 
constructed ? the atmospheric engine because half of the work 
was done by the pressure of the atmosphere, namely, the down¬ 
ward motion of the piston. 

What improve- 761. The celebrated Mr. James Watt intro- 
^Watt make in ^ ucet ^ two important improvements into the steam- 
the stcam-en- engine. Observing that the cooling of the cylinder 
R ins ■ by the water thrown into it to condense the steam 

lessened the expansibility of the steam, he contrived a method 
to withdraw the steam from the principal cylinder, after it had 
performed its office, into a condensing-chamber, where it is recon-' 
verted into water, and conveyed back to the boiler. The other 
improvement, called the double action , consjsts in substituting 
the expansive power of steam for the atmospheric pressure. This 
was performed by admitting the steam into the cylinder above 
the raised piston, at the same moment that it is removed from 
beloiv it; and thus the power of steam is exerted in the descend¬ 
ing as well as in the ascending stroke of the piston ; and a much 
greater impetus is given to the machinery than by the forme* 
method. From the double action of the steam above , as well as 
beloiv the piston, and from the condensation of the ste^m after 
it has performed its office, this engine is called Watt’s double- 
ding condensing steam-engine. [See also , No. 766.] 

Explain 762. Fig. 108 represents that portion of the st~£m- 
lig. 108. en gj ne j n w hich steam is made to act, and propel such 
machinery as may be connected with it It also exhibit* two 

17 * 


U) 8 


NATURAL PHILOSOPHY. 



improvements of* Mr. Watt. 

The principal Darts are the 
boiler, the cylinder and its 
piston, the condenser, the 
air-pump, the steam-pipe, 
the eduction-pipe, and the 
cistern. In this figure, A 
represents the boiler, G 
the cylinder, with H the 

piston, B the steam-pipe, with two branches * communicating 
with the cylinder,' the one above and the other below the piston. 
This pipe has two valves, Fand G, which are opened and closed 
alternately by machinery connected with the piston. The steam 
is carried through this pipe by the valves, when open, to the 
cylinder, both above and below the piston. K is the eduction- 
pipe, having two branches, like the steam-pipe, furnished with 
valves, &c., which are opened and shut by the same machinery. 
By the eduction-pipe the steam is led off from the cylinder, as 
the piston ascends and descends. 

L is the condenser, and 0 a stop-cock for the admission of cold 
water. M is the pump. N is the cistern of cold water in which 
the condenser is immersed. R is the safety-valve. When the 
valves are all open, the steam issues freely from the boiler, and 
circulates through ail the parts of the machine, expelling the 
air. This process is called blowing out, and is heard when a 
steamboat is about starting. 

Now, the valves F and Q being closed, and G and P remain¬ 
ing open, the steam presses upon the piston and forces it down 
As it descends, it draws with it the end of the working-beam, 
which is attached to the piston-rod J (but which is not repre 
Rented in the figure). To this working-beam (which is a lever 
of the first kind) bars or rods are attached, which, rising and 
falling with the beam and the piston, open the stop-cock 0, ad- 


* The steam and the eduction pipes are sometimes made in forms differing 
from those in the figure, and they differ much in different engines. 





















bTEAM-ENGINE. 


liw 

nutting a stream of cold water, which meets the steam from the 
cylinder and condenses it, leaving no force below the pistot to 
oppose its descent. At this moment the rods attached to the 
working-beam close the stop-cocks G and P, and open F and Q. 
The steam then flows in below the piston, and rushes from above 
it into the condenser, by which means the piston is forced up 
again with the same power as that with which it descended. 
Thus the steam-cocks G and P and F and Q are alternately 
opened and closed; the steam passing from the boiler drives the 
piston alternately upwards and downwards, and thus produces 
a regular and continued motion. This motion of the piston, 
being communicated to the working-beam, is extended to other 
machinery, and thus an engine of great power is obtained. 

The pump M, the rod of which is connected with the working- 
beam, carries the water from the condenser back into the boiler 
by a communication represented in Fig. 109. 

The safety-valve it, connected with a lever of the second 
kind, is made to open when the pressure of the steam within the 
boiler is too great. The steam then rushing through the aperture 
under the valve, removes the danger of the bursting of the boiler. 

How is the 763. The power of a steam-engine is gen- 
^team-engine erally'expressed by the power of a horse, 
estimated? which can raise 33,0U0 lbs. to the height of 
one foot in a minute. An engine of 100 horse power is 
one that will raise 3,300,000 lbs. to the height of one foot 
in one minute. 

What are the 764. The steam-engine is constructed in va- 

two hinds of r ; ous forms, and no two manufacturers follow- 
stcam-engines , . 

and how do they ing exactly the same pattern; but the two pnn- 

differ? cipal kinds are the high and the low pressure 

engines, or, as they are sometimes called, the non-condensing and 

the condensing engines. The non-condensing or high-pressure 

engines differ from the low-pressure or condensing engines u 

having no condenser. The steam, after having moved the piston. 


200 


.NATURAL PHILOSOPHY. 


is let off into the open air. 4s this kind of engine occupies less 
space, and is much less complicated, it is generally used on rail¬ 
roads. In the low-pressure or condensing engines, the steam, 
after having moved the piston, is condensed, or converted inio 
water, and then conducted back into the boiler. 

, 765. The steam-engine, as it is constructed 

Who were the ° 

principal im- at the present day, is the result of the inventions 
provers of the and discoveries of a number of distinguished indi- 
steam-engine? v jd U als, a ^ different periods. Among those who 
have contributed to its present state of perfection, and its ap¬ 
plication to practical purposes, may be mentioned the names of 
Somerset, the Marquis of Worcester, Savery, Newcomen, Fulton, 
and especially Mr. James Watt. 

766. To the inventive genius of Watt the engine is indebted for 
the conde?iser , the appendages for parallel z notion , the application of 
the governor , and for the double action. In the words of Mr. Jeffrey, 
it may be added, that, “ by his admirable contrivances, and those of 
Mr. Fulton, it has become a thing alike stupendous for its force and 
its flexibility; for the prodigious power it can exert, and the ease 
and precision and ductility with which it can be varied, distributed, 
and applied. The trunk of an elephant, that can pick up a pin, or 
rend an oak, is as nothing to it. It can engrave a seal, and crush 
masses of obdurate metal before it; draw out, without breaking, a 
thread as fine as gossamer, and lift up a ship of war like a baublo 
in the air. It can embroider muslin, and forge anchors ; cut steel 
into ribands, and impel loaded vessels against the fury of the winds 
and waves.” 

Explain 767. Fig. 109 represents Watt’s double-acting eondens- 
hg. 109. j n g s team-engine, in which A represents the boiler, con¬ 
taining a large quantity of water, which is constantly replaced as 
fast as portions are converted into steam. B is the steam-pipe, 
conveying the steam to the cylinder, having a steam-cock b to 
admit or exclude the steam at pleasure. 

C is the cylinder, surrounded by the jacket c c, a space kept 
constantly supplied with hot steam, in order to keep the cylinder 
from being cooled by the external air. D is the eduction-pipe, 
communicating between the cylinder and the condenser. E is 
the condenser, with a valve e called the injection-cock, admitting 


STEAM-ENGINE. 


2 °! 

a jet of cold water, which meets the steam the instant that the 
steam enters the condenser. F is the air-pump, which is a com¬ 
mon suction-pump, but is here called the air-pump because it 
removes from the condenser not only the water, but also the air, 
and the steam that escapes condensation. G G is a cold-water 
cistern, which surrounds the condenser, and supplies it with cold 
water, being filled by the cold-water pump, which is represented 


Fig. 109. 



densation from the hot well to the boiler. 

L L are levers, which open and shut the valves in the chan 
nel between the steam-pipe, cylinder, eduction-pipe, and con¬ 
denser ; which levers are raised or depressed by projection# 
attached to the piston-rod of the pump. M M is an apparatus 
for changing the circular motion of the working-beam into par* 






























202 


NATURAL PHILOSOPHY. 




















































































STEAM-ENGINE. 


a)iel motion, so that the piston-rods are made to move in a straight 
line. N N is the working-beam, which, being moved by the 
rising and falling of the piston attached to one end, communi¬ 
cates motion to the fly-wheel by means of the crank P, and from 
the fly-wheel the motion is communicated by bands, wheels or 
levers, to the other parts of the machinery. 0 0 is the governor. 

The governor, being connected with the fly-wheel, is made to 
participate the common motion of the engine, and the balls will 
remain at a constant distance from the perpendicular shaft so 
long as the motion of the engine is uniform; but, whenever the 
engine moves faster than usual, the balls will recede further from 
the shaft, and by partly closing a valve connected with the 
l >oiler, will diminish the supply of steam to the cylinder, and 
[bus reduce the speed to the rate required. 

The steam-engine thus constructed is applied to boats to turn 
wheels having paddles attached to their circumference, which 
answer the purpose of oars. [See Fig. 110.] It is used also 
in work-shops, factories, &c.; and different directions and veloc¬ 
ities may be given to the motion produced by the action of the 
steam on the piston, by connecting the piston to the beam with 
wheels, axles and levers, according to the principles stated 
under the head of Mechanics. 

Steamboats are used principally on rivers, in harbors, bays, and on 
the coast. They are made of all sizes, and carry engines of different 
power, proportioned to the size of the boat. 

The steamship [See Fig. Ill], in addition to its steam-engines 


Fig. ill. 







204 


NATURAL PHILOSOPHY. 


What is the 
locomotive 
steam-engine 1 


and paddles, is rigged with masts and sails to increase the speed, oi 
to make progress if the engines get out of order. 

The Propeller differs from a steam-boat or steam-ship, by haying 
an immense screw projecting from under the stern of the ship, instead 
of paddle-wheels. The screw is caused to revolve by means of steam- 
engines, and forces the vessel forward by its action on the water. 

V' 768. The locomotive engine is a high- 
pressure steam-engine, mounted on wheels, 
and used to draw loads on a railroad, ei other 
level road. It is usually accompanied by a large wagon, 
called a tender , in which the wood and water used by the 
engine are carried. 

Explain 769. Fig. 112 represents a side view of the mto/ r.a) 
112. cons t ruc tion of a locomotive steam-engine; in which 
F represents the fire-box, or place where the fire is k pt; P 
the door through which the fuel is introduced. The spaces 
marked B are the interior of the boiler, in which tin,' water 
stands at the height indicated by the dotted line. Tho V oiler is 
closed on all sides, all its openings being guarded by valves. 
The tubes marked p p conduct the smoke and flame of the fuel 
through the boiler to the chimney C C, serving, at the same 
time, to communicate the heat to the remotest part of the boiler. 
By this arrangement, none of the heat is lost, as these tubes are 
all surrounded by the water. S S S is the steam-pipe, open at 
the top V S, having a steam-tight cock, or regulator, V, which 
is opened and shut by the lever L, extending outside of the 
boiler, and managed by the engineer. 

The operation of the machine is as follow s: The steam being 
generated in great abundance in the boiler, and being unable to 
escape out of it, acquires a considerable degree of elastic force. 
If at that moment the valve V be opened, by the handle L, the 
steam, entering the pipe S, passes in the direction of the arrow, 
through the tube, and enters the valve-box at X. There a 
sliding-valve, which moves at the same time with the machine, 
opens for the steam a communication successively with each end 
of the cylinder below. Thus, in the figure, the entrance on the 
right hand of the sliding-valve is represented as being c >pen, and 


VIEW OP TIIE INTERNAL CONSTRUCTION OF UINKLEY & DRURl'S LOCOMOTIVE STEAM-ENGINE. 


STEAM-ENGINI5. 



18 


til -an 





















































































































Me. 118 


2 06 



NATURAL PHILOSOPHY 




































































































STEAM ENGINE. 


201 



flifr. 114. 

























































































































































































































Pig. 115 


208 


NATURAL PHILOSOPHY. 

















































STEAM-ENGINE. 


2t>9 


the steam follows in the direction of the arrows into the cylinder, 
where its expansive force will move the piston P in the diree* 
tion of the arrow. The steam or air on the other side of the 
piston passes out in the opposite direction, and is conveyed by a 
tube passing through C C into the open air. 

The motion of the piston in the direction of the arrow causes 
the lever N to close the sliding-valve on the right, and open a 
communication for the steam on the opposite side of the piston 
P, where it drives the piston back towards the arrow, at the 
same time affording a passage for the steam on the right of the 
piston to pass into the open air. 

Motion being thus given to the piston, it is communicated, by 
means of the rod R and the beam Gr, to the cranks K K, which, 
being connected with the axle of the wheel, causes it to turn, 
and thus move the machine. 

Thus constructed, and placed on a railroad, the locomotive 
steam-engine is advantageously used as a substitute for horse 
power, for drawing heavy loads. 

The apparatus of safety-valves, and other appliances for the 
management of the power produced.by the machine, are the 
same in principle, though differing in form, with those used in 
other steam-engines; for a particular description of which, the 
student is referred to practical treatises upon the subject: 


„„ , . 770. The Stationary Steam-engine.- 

What is the 

best form of This engine is generally a high-pressure or 

the steam-en- non _condensing engine, used to propel ma- 
gine? . ° ° r r 

chinery in work-shops and factories. As it is 

designed for a labor-saving machine, it is desirable to com¬ 
bine simplicity and economy with safety and durability in 
its construction ; and that form of this engine is to be pre¬ 
ferred which in the greatest degree unites these qualities. 


Describe the Sta- 771. The figure on page 207 represents 
tionary Steam - Tufts’ stationary steam-engine,* with sections ol 
m S ine the interior. Like the double-acting condens- 


♦ Tbif engine was constructed by Mr Otis Tufts, of East Boston. Mus- 
18* 


210 


NATURAL PHILOSOPHY. 


ing engine of Mr. Watt, desciibed in Fig. 109, it is furnished 
with a governor, by which the supply of steam is regulated* 
and, like the locomotive, Fig. 112, the cylinder, with its piston, 
has a horizontal position. The steam is admitted into the valve- 
box through an aperture at E, in the section , and from thence 
passes into the cylinder through a sliding-valve, alternately to 
each side of the piston P, as is represented by the direction of 
the arrows, the sliding-valve being moved by the rod V, commu¬ 
nicating with an “ eccentric ” apparatus attached to the axis of 
the fly-wheel. The direction of the current of steam to the 
valve-box is represented by the arrow at I, and its passage out¬ 
ward from the cylinder, after it has moved the piston, is seen at 
O. In this engine there is no working-beam, as in Watt’s 
engine, Fig. 109, but the motion is communicated from the pis¬ 
ton-rod to a crank connected with the fly-wheel, which, turning 
the wheel, will move all machinery connected either with the 
axle or the circumference of that wheel. 

Fig. 115 represents the Locomotive Steam-engine in one of 
its most perfect forms, as used on railways at the present day. 

772. Optics. — Optics is the science which 


-V 


What is Optics ? 


treats of light, of colors, and of vision. 


How arc all sub- 773. The science of Optics divides all sub 

stances consul- stances into the following classes: namely, 
ered in Optics l , . , , 

luminous, transparent, and translucent; re¬ 
flecting, refracting, and opaque. 


What are lumi¬ 
nous bodies l 


774. Luminous bodies are those which 
shine by their own light; such as the sun, 
the stars, a burning lamp, or a fire. 


sochusetts. It is the engine used to propel the machinery at a late Fair 
of the Massachusetts Mechanic Association, where it was very highly and 
justly commended for its beauty and simplicity of construction, and tLe 
perfectly “ noiseless tenor of its way.” The figure whieh represents it is an 
electrotype copy of a steel plate, designed by Brown &■ Harbrys, under the 
direction of Mr. Tufts. The electrotype copy was taken by Mr. A. Wilcox, 
Washington-street. Boston. The electrotype process will be noticed in a 
subsequent page of this volume. 


OPTIC*. 


‘211 


What are trans¬ 
parent sub¬ 
stances ? 

through them; 


775. Transparent substances are those 
which allow light to pass through them 
freely, so that objects can be distinctly seen 
as glass, water, air, &c.* 


776. Translucent bodies are those which 

luctntTolls™' P crmit a P ortion of I'ght to pass through 
them, but render the object behind them in¬ 
distinct; as horn, oiled paper, colored glass, &c. 


What are re- 777. Reflecting substances are those which 
fleeting sub- do not permit light to pass through them; 

but throw it off in a direction more or less 
oblique, according as it falls on the reflecting surface*; as 
polished steel, looking-glasses, polished metal, &c. 

778. Refracting substances are those which 

v r IlClt CIV6 T6- ^ 

fracting sub- turn ^ ie light from its course in its passage 
stances ? through them; and opaque substances are 

those which permit no light to pass through them, as met¬ 
als, wood, &c. 

What is light? 779. It is not known what light is. Sir 

What are the j saac Newton supposed it to consist of 
two tncones re- 

specting the na- exceedingly small particles, moving from 
ture oj ught ? luminous bodies; others think that it con¬ 
sists of the undulations of an elastic medium, which fills 
all space.f These undulations (as is supposed) produce the 


* No substaace that exists on our earth is perfectly transparent, and light 
must, therefore, necessarily be impaired in its passage through all transpa¬ 
rent media, and the diminution it suffers will vary as the medium is more 
or less transparent, and as the passage it makes is of greater or less length. 
The exact ratio in which light is diminished has not yet been determined ; 
it is, however, an established fact, that even those bodies which approach 
most nearly to perfect transparency become opaque when their thickness is 
Considerably increased. 

+ These two theories of light are called respectively the corpuscular and 
the undulalory theory. By the former the reflection of light is supposed tc 
take place in the same manner as the reflection of solid elastic bodies, as 
has been explained under the head of Mechanics [see No. 165, page 49] 
By the latter the propagation of light takes place from every luminous 
poiut. by means of the undulatory movements of the ether. On this hypoth- 


« 


212 


NATURAL PHILOSOPHY. 


sensat’on of light to the eye, in the same manner as the 
vibrations of the air produce the sensation of sound to the 
ear. The opinions of philosophers at the present day are 
inclining to the undulatory theory. 

What is a ray 780. A ray of light is a single line of 
of light? light proceeding from a luminous body. 

781. Kays of light are said to diverge 

fid'lo diverge 5 ! wllen the y separate more Fi g . no. 

widely as they proceed 
from a luminous body. 

Fig. 116 represents the 
Explain Fig. ra ^ g j^t diverging as they proceed from the 

luminous body, from F to D. 

782. It. will be seen by this figure that, as light is projected In 
every direction, its intensity must decrease with the distance, and 
this decrease is determined by a fixed law. The light received upon 
any surface decreases as the square of the distance increases. 
Tims, if a portion of light fall on a surface at the distance of two 
feet from any luminary, a surface twice that distance will receive 
only one-fourth as much light; at three times that distance, one- 
ninth ; at four times the distance, one-sixteenth, &c. Hence a per¬ 
son can see to read at a short distance from a single lamp much 
better than at twice the same distance with two lamps, &c. 

to converge 

The point 

esis, the waves of light follow the general laws of the reflection of all 
elastic fluids , and, accordingly, every wave from every point, when it im¬ 
pinges on any resisting object so as to be reflected, forms a new wa ve in its 
course back, having its centre as much on the other side of the obstacle as 
the centre of the original wave was on this side. In the case of light the 
centre of the original wave is, obviously, the luminous point. There is a 
remarkable similarity, therefore, between the reflection of light, snd echo , 
or the reflection of sound. It has been shown, under the head of Acoustics, 
that when two waves meet under certain circumstances, the elevation of 
one wave exactly filling up the depression of another wave, produces wha,* 
is called the acoustic paradox, namely, two sounds producing silence. It wil’ 
readily be seen that the same undulatory movements in Optics will produce 
the same analogous effect ; or, in other words, that two rays of light may 
produce darkness ; and this may, with equal propriety, be termed the optical 
paradox. But a clear understanding of the principles involved in what 
is called respectively the hydrostatic, pneumatic, acoustic and optical para 
dox, shows that there is no paradox at all, but that each is the necessary 
result of certain fixed and determinate laws 


When are rays 
of light said to 
converse ? 


. 783. Buys of light are said 

when they approach each other. 








OPTICS. 


213 


Pig. 117. 


at which converging rays meet is called 
the focus. 

Fig. 117 represents con¬ 
verging rays of light, of 
which the point F is the focus. 

784. A beam of Fig - 118 ' 

light consists of many 
rays running in parallel lines. 


Fry lain Fig. 

117. 


What, is a beam 
of light ? 



Explain Fig. 

118. 


Fig. 118 represents a beam of light. 

785. A pencil of rays is a collection of 
diverging or converging rays. [/S'ee Figs. 
116 and 117.] 

786. Light proceeding from a luminous 
body is projected forward in straight lines in 
every possible direction. It moves with a 
rapidity but little, short of two hundred thou¬ 
sand miles in a second of time. 


What is a pen¬ 
cil of rays l 


In what direc¬ 
tion, and with 
what rapidity, 
does light move l 


From what part 
of a luminous 


787. Every point of a luminous body is 


a centre, from which light radiates 


m every 


body does light direction. Rays of light proceeding from 
proceed. different bodies cross each other without 

interfering. The rays of light which issue from terrestrial 
bodies continually diverge, until they meet with a refract¬ 
ing substance, nut the rays of the sun diverge so little, on 
account of the immense distance of that luminary, that they 
are considered parallel. 

788. A shadow is the darkness produced bj 
shadow™ a ^e intervention of an opaque body, which pre¬ 
vents the 'ays of light from reaching an object 
behind the opaque body. 

789. Shadows are of different degrees of 


Why are shad¬ 
ows of different 


darkness, because the light from other lump 





214 


NATURAL PHILOSOPHY. 


degrees of dark- nous bodies reaches the spot ay here the 

shadow is formed. * Thus, if a shadow be 
formed when two candles are burning in a room, that 
shadow will be both deeper and darker if one of the can¬ 
dles be extinguished. The darkness of a shadow is propor¬ 
tioned to the intensity of the light, when the shadow is 
produced by the interruption of the rays from a single 
luminous body. 

mat produce, . 790 - As the de g ree of 1! g ht and darkness 
the darkest can be estimated only by comparison, the 

strongest light will appear to produce the 
deepest shadow. Hence, a total eclipse of the sun occa¬ 
sions a more sensible darkness than midnight, because it is 
immediately contrasted with the strong light of day. Hence, 
also, by causing the shadow of a single object to be thrown 
on a surface, — as, for instance, the wall,—from two or mors 
lights, we can tell which is the brightest light, because it 
will cause the darkest shadow. 


791. When a luminous body is larger than 
shape of the an opaque body, the shadow of the opaque 
shadow of an body will gradually diminish in size till it 


opaque body . terminates in a point. The form of 

shadow of a spherical body will be that of a cone. 


the 


Fig. 119. A repre- 
Fxplain Fig. gentg t h e gunj Pn( j ]3 

the moon. The sun 
being much larger than the moon, 
causes it to cast a converging shadow, 
which terminates at E. 


Fig. 119. 



792. When the luminous body is smaller than the 
',-paque body, the shadow of the opaque body will gradually 
increase in size with the distance, without limit. 


OPTICS. 


915 


3.x Fig. 120 the shadow Fi s- 12 °* 

of the* object A increases 
in size at the different dis¬ 
tances B, C, D, E; or, in 
other words, it constantly 
diverges. 

793. When several luminous bodies shine upon the same 
object, each one will produce a shadow. 



What is it the 
abject of Fig. 
121 to show ? 


Fig. 121 represents a ball A, illuminated by 
the three can¬ 


dles B, C, and 
D. The light B produces the 
shadow b, the light C the shadow 
c, and the light I) the shadow d ; 
but, as the light from each of the 
candles shines upon all the shad¬ 
ows except its own, the shadows 
will be faint. 


rig. lai. 



What becomes of 
the light which 
falls on an 
opaque object ? 


When is light 
said to be re¬ 
fected? 


794. When rays of light fall upon an 
opaque body, part of them are absorbed, and 
part are reflected. 

Light is said to be reflected when it is 
thrown off from the body on which it falls; 
and it is reflected in the largest quantities 
from the most highly polished surfaces. Thus, althougli 
most substances reflect it in a degree, polished metals, look- 
ing-glasses, or mirrors, &c., reflect it in so perfect a man¬ 
ner as to convey to our eyes, when situated in a proper 
position to receive them, perfect images of -whatever objects 
shine on them, either by their own or by borrowed light. 

795. That part of the science of Optics 
which relates to reflected light is called 
Catoptrica. 


What is Catop- 
trv^s ? 


















ilfl 


NATURAL PHILOSOPHY. 


What is the fun- ? 96. The laws of reflected light are the 

i lamental law of same as those of reflected motion. Thus, 
Catoptrics f when light falls perpendicularly on an 

opaque body, it is reflected back in the same line towards 
the point whence it proceeded. If it fall obliquely, it will 
be reflected obliquely in the opposite direction; and in all 
cases the angle of incidence will be equal to the angle of 
reflection. This is the fundamental law of Catoptrics, or 
reflected light. 

797. The angles of incidence and reflection have already beer 
described under the head of Mechanics [see explanation of 
Fig. 10, No. 1<32]; but, as all the phenomena of reflected light 
depend upon the law stated above, and a clear idea of these 
angles is necessary in order to understand the law, it is deemea 
expedient to repeat in this connection the explanation already 
given. 

An incident ray is a ray proceeding to or falling on any sur¬ 
face ; and a reflected ray is the ray which proceeds from any 
reflecting surface. 

Fig. 122 is designed to show 
f.rplain Fig. q ie an g] es G f incidence and of 

reflection. Tn this figure, M 
A M is a mirror, or reflecting surface. P is 
a line perpendicular to the surface. I A rep¬ 
resents an incident ray, falling on the mirror 
*n such a manner as to form, with the perpen¬ 
dicular P, the angle I A P. This is called 
the angle of incidence. The line R A is to 
be drawn on the other side of P A in such a manner as to have 
the same inclination with P A as I A has : that is, the angle 
K A P is equal to I A P. The line R A will then show the 
course of the reflected ray; and the angle RAP will be 
the angle of reflection. 

From whatever surface a ray of light is reflected, —whether it 
be a plain surface, a convex «?rfaee, or a concave surface, — this 





OPTICS. 


217 


jiw invariably prevails; so that, if we notice the. inclination of 
any incident ray, and the situation of the perpendicular to the 
surface on which it falls, we can always determine in what man¬ 
ner or to what point it will be reflected. This law explains the 
reason why, when we are standing on one side of a mirror, we 
can see the reflection of objects on the opposite side of the room, 
but not those on the same side on which we are standing. It also 
explains the reason why a person can see his whole figure in a 
mirror not more than half of his height. It also accounts for 
all the apparent peculiarities of the reflection of the different 
kinds of mirrors. / 


How are lu¬ 
minous and 
opaque bodies 
respectively 
seen ? 


[ 8 . Opaque bodies are seen only by re¬ 
fected light. Luminous bodies are seen by 
the rays of light which they send directly to 
our eyes. 


What effect 799 . All bodies absorb a portion of the light 
thfinicn- which they receive ; therefore the intensity of 
sity of light / light is diminished every time that it is reflected. 
What does 800. Every portion of a reflecting surface 
€ qf ^reflecting reflects an entire image of the luminous body 
surface refect ? shining upon it. 


W r 7 » When the sun or the moon shines upon a 

XX hy do we r 

not see many sheet of water', every portion of the surface reflects 
images^ of the an en ti r e image of the luminary; but, as the image 
refected by a can seen on ^y ky reflected rays, and as the 
refecting sur- angle of reflection is always equal to the angle of 
? incidence, the image from any point can be t een 

only in the reflected ray prolonged. 


Why do objects 801. Objects seen by moonlight appea’ winter 
appear fainter than when seen by daylight, because th. fight by 
by moonlight l w j 1 j c | 1 are seen h as been twice reflected ; for, 
the moon is not a luminous body, but its light is caused by the 
sun shining upon it. This light, reflected from the moon and 
falling upon any object, is again reflected by that object. It 
19 


218 


NATURAL FHILOSOIIIY. 


buffers, therefore, two reflections; and since a portion is absorbed 
by each surface that reflects it, the light must be proportion 
««ily fainter. In traversing the atmosphere, also, the rays both 
of the sun and moon, suffer diminution; for, although pure air 
is a transparent medium, which transmits the rays of light 
freely, it is generally surcharged with vapors and exhalations, 
by which some portion of light is absorbed. 

„„ . 802. All objects are seen by means of the 

When is an J J . _ . 

object invisi - rays of light emanating or reflected from them ; 

• and therefore, when no light falls upon an 

opaque body, it is invisible. 

This is the reason why none but luminous bodies can be 
seen in the dark. For the same reason, objects in the shade or 
in a darkened room appear indistinct, while those which are 
exposed to a strong light can be clearly seen. We see the 
things around us, when the sun does not shine directly upon them, 
solely by means of reflected light. Everything on which it 
shines directly reflects a portion of its rays in all possible direc¬ 
tions, and it is by means of this reflected light that we are 
enabled to see the objects around us in the day-time which are 
not in the direct rays of the sun. It may here also be remarked 
that it is entirely owing to the reflection of the atmosphere that 
the heavens appear bright in the day-time. If the atmosphere 
had no reflective power, only that part would be luminous in 
which the sun is placed ; and, on turning our back to the sun, the 
whole heavens would appear as dark as in the night; we should 
have no twilight, but a sudden transition from the brightest 
sunshine to darkness immediately upon the setting of the sun. 

803. When rays of light, proceeding from 
Hou cU rays . . ,, , 

of light si.'er an J object, enter a small aperture, they cross 

a small ayer- 0 ne another, and form an inverted image of the 
ture. * . . mi • . ° „ 

object. I his is a necessary consequence of the 
law that light always moves in straight lines. 

hlrplain ‘ &04. Fig. 123 represents the rays from an object, 

123. a c, entering an aperture. The ray from a pa;>e? 


OPTICS. 


21 U 


wwn through the aperture to d, and the ray from t passes 
up to h, and thus these rays, crossing at the aper- ri & 
ture, form an inverted image on the wall. The 
room in which this experiment is made should be 
darkened, and no light permitted to enter, except¬ 
ing through the aperture. It then becomes a 
camera obscura. 



805.- These words signify a darkened chamber. In the future de 
eeription which will be given of the eye, it will be seen that the 
camera obscura is constructed on the same principle as the eye. If a 
convex lens be placed in the aperture, an inverted picture, not only 
of a single object, but of the entire landscape, will be found on the 
'‘wall. A portable camera obscura is made by admitting the light 
into a box of any size, through a convex lens, which throws the 
image upon an inclined mirror, from whence it i3 reflected upwards 
to a plate of ground glass. In this manner a beautiful but dimin¬ 
ished image of the landscape, or of any group of objects, is present¬ 
ed on the plate in an erect position. 

806. The angle of vision is the angle formed 


What is the 
angle of 
vision ? 

What is the 
object of 
figures 124 
and 125 1 


at the eye by two lines drawn from opposite 
parts of an object. 

807. The angle C, in Fig. 124, repiesents the 
angle of vision. The line A G, proceeding from 
one extremity of the object, meets the line B C 
from the opposite extrem- rig. 124. 

ity, and forms an angle C 
at the eye ; — this is the 
angle of vision. 

808. Fig. 125 represents 
the different angles made 
by the same object at dif- • 
ferent distances. From an inspection of 
the figure, it is evident that the nearer 
the object is to the eye, the wider must c 
be the opening of the lines to admit the 
extremities of the object, and, consequent¬ 
ly, the larger the angle under which it is seen ; and, on the con 
trary, that objects at a distance will form small angles of vision 
Thus, in this figure, the three crosses F G, D h. and A !•>. art 











520 


NATURAL PHILOSOPHY. 


ail of the same size ; but A B, being the most distant, subtends 
the smallest angle A C B, while D E and F G, being nearei to 
the eye, situated at C, form respectively the larger angles BCE 
and FOG. 

809. The apparent size of an object depends upon 
On what does , 0 , ,. . . , 

the apparent “ ie size °* ta e an g* e vision. But we are accus- 

size of an oh- tomed to correct, by experience, the fallacy of ap- 
ject depend? p earances ; and, therefore, since we know that real 
objects do not vary in size, but that the angles under which we 
see them do vary with the distance, we are not deceived by the 
variations in the appearance of objects. 

Thus, a house at a distance appears absolutely smaller than the 
window through which we look at it; otherwise vve could not see 
it through the window; but our knowledge of the real size of the 
house prevents our alluding to its apparent magnitude. In Fig. 124 
i‘; will be seen that the several crosses, A B, D E, F G, and II I, 
although very different in size, on account of their different distances, 
subtend the same angle A C B ; they, therefore, all appear to the 
eye to be of the same size, while, in Fig. 125, the three objects A B, 
I) E, and F G, although of the same absolute size, are seen at a dif¬ 
ferent angle of vision, and they, therefore, will seem of different 
sizes, appearing larger as they approach the eye. 

It is to a correct observance of the angle of vision that the art of 
perspective drawing is indebted for its accuracy. 

When is an 810. When an object, at any distance, does 
°onaccount of not subtend an angle of more than two seconds 
5 distance 1 0 f a degree, it is invisible. 

At the distance of four miles a man of common stature 
will thus become invisible, because his height at that distance 
will not subtend an angle of two seconds of a degree. The size 
of the apparent diameter of the heavenly bodies is generally 
stated by the angle which they subtend. 

When is mo- ®11. ^ ien tbs velocity of a moving body 
tion imper- does not exceed twenty degrees in an hour, its 
teptille! motion is imperceptible to the eye. 

It is for this reason that the motion of the heavenly 
bodies is invisible, notwithstanding their immense velocity. 

812. The real velocity of a body in motion round a point de¬ 
pends on the space comprehended in a degree. The more dis* 


/ 


OPTICS. 


221 


tant the moving body from the centre, or, in other words, the 
larger the circle which it has to describe, the larger will be the 
degree. 

813. In Fig. 126, if the man at A, and the 
man at B, both start together, it is manifest 
that A must move more rapidly than B, to 
arrive at C at the same time that B reaches 
I), because the arc A C is the arc of a larger 
circle than the arc B D. But to the eye at E 
the velocity of both appears to be the same, C ” E 
oecause both are seen under the' same angle of vision. 


Fig. 126. 



What are ^ m * rror a sm0 °th and polished sur- 

mirrors , and face, that forms images by the reflection of the 
made V ^ ra d s light. Mirrors (or looking-glasses) are 
made of glass, with the back covered with an 
amalgam, or mixture of crifiercury and tin foil. It is the 
smooth and bright surface of the mercury that reflects the 
rays, the glass acting only as a transparent case, or cover¬ 
ing, through which the rays find an easy passage. Some 
of the rays are absorbed in their passage through the glass, 
because the purest glass is not free from imperfections. For 
this reason, the best mirrors are made of an alloy of copper 
and tin, called speculum metal. 


What are the 815. There are three kinds of mirrors, 
different kinds namely, the plain, the concave, and the con- 

of mirrors! yex 


Plain mirrors are those which have a flat surface, such 
as a common looking-glass ; and they neither magnify nor 
diminish the image of objects reflected from them. 

816. The reflection from plain mirrors is always 
^re 'objects re- obedient to the law that the angles of incidence and 
fleeted from a reflection are equal. For this reason, no person 
looking glass ? can gee another in a looking-glass, if the other can 
not see him in return. 

19 * 



222 


tU’CUftAL PHILOSOHIY. 


How do look- 817. l ooking-glasses or plain mirrors cause 
make allotj ecu ^ry thing to appear reversed. Standing before a 
appear ? looking-glass, if a person holds up his left hand it 

will appear in the glass to be the right. 

818. A looking-glass, to reflect the whole person, needs be but half 
of the length of the person. 

819. When two plain mirrors stand opposite to each other, the 
reflections of the one are cast upon the other, and to a person be¬ 
tween them they present a long-conrinued vista. 

820. When two reflecting surfaces are inclined at an angle, the 
reflected objects appear to have a common centre to an eye viewing 
them obliquely. 1* is on this principle that the kaleidoscope is 
constructed. 

What is a 821. The Kaleidoscope consists of two reflecting 
Kaleidoscope ? surfaces, or pieces of looking-glass, inclined to 
each other at an angle of sixty degrees, and placed between 
the eye and fhe objects intended to form the picture. 

The two plates are enclosed in a tin or paper tube, and the 
objects, consi jting of pieces of colored glass, beads, or other 
highly-colored fragments, are loosely confined between two cir¬ 
cular piece' 1 , of common glass, the outer one of which is slightly 
ground, to make the light uniform. On looking down the tube 
through r> small aperture, and where the ends of the glass plates 
nearly meet, a beautiful figure will be seen, having six angles, 
the reflectors being inclined the sixth ^art of a circle. If in¬ 
clined the twelfth part or twentieth part of a circle, twelve or 
twerty angles will be seen. By turning the tube so as to alter 
the position of the colored fragments within, these beautiful forms 
will be changed ; and in this manner an almost infinite variety 
r** patterns may be produced. 

The word Kaleidoscope is derived from the Greek language, and 
means “ the sight of a beautiful form.” The instrument was in¬ 
vented by Dr. Brewster, of Edinburgh, a few years ago. 

822. A convex mirror is a portion of the external sur¬ 
face of a sphere. Convex mirrors have therefore a convex 
surface. 

823 A concave mirror is a portion of the inner surface 


OPTICS. 




Concave mirrors have therefore a con- 


N represents both a convex 
They are both a portion of a 
The outer part of M N is a 
Fig. 127. 

O 

V 



of a hollow sphere, 
cave surface. 

Explain 824. In Fig. 127, M 
tig. 127. and a concave mirror, 
sphere of which 0 is the centre, 
convex, and the inner part is 
a concave mirror. Let A B, 

C D, E F, represent rays 
falling on the convex mirror 
M N. As the three rays are 
parallel, they would all be per¬ 
pendicular to a plane or flat 
mirror; but no ray can fall 
perpendicularly on a concave 
or convex mirror which is not 

directed towards the centre of the sphere of which the mirror is 
a portion. For this reason, the ray C D is perpendicular to the 
mirror, while the other rays, A B and E F, fall obliquely upon 
it. The middle ray therefore, falling perpendicularly ou the 
mirror, will be reflected back in the same line, while the two 
other rays, falling obliquely, will be reflected obliquely ; namely, 
the ray A B will be reflected to Gr, and the ray E F to H, and 
the angles of incidence A B P and EFT will be equal to the 
angles of reflection P B G and T F H; and, since we see objects 
in the direction of the refected rays , we shall see the image at 
L, which is the point at which the reflected rays, if continued 
through the mirror, would unite and form the image. This point 
is equally distant from the surface and the centre of the sphere, 
and is called the imaginary focus of the mirror. It is called the 
imaginary focus, because the rays do not really unite at that 
point, but only appear to do so; for the rays do not pass through 
the mirror, since they are reflected by it. 

^25. The image of an object reflected fiom a convex 
mirror is smaller than the object 






NATURAL PHILOSOPHY. 


224 


\A T hat is the 
object of 
Fig. *28 ? 


826. This is owing to the divergence of the re 
fleeted rays. A convex mirror converts, by ref.ee 
ti&n , parallel rays into dive' ent rays - ays that 


fall upon the mirror divergent are render mi btiil more diver• 
gent by reflection, and convergent rays are reflected either 
parallel, or less con- Pig. 128. 

vergent. If, then, an 
object, A B, be placed 
before any part of a 
convex mirror, the 
two rays A and B, 
proceeding from the 
extremities, falling 
convergent on the 
mirror, will be re¬ 
flected less convergent, and will not come to a focus until they 
arrive at G ; then an eye placed in the direction of the reflected 
rays will see the image formed in (or rather behind) the mirror 
at a b ; and, as the image is seen under a smaller angle than the 
object, it will appear smaller than the object. 



What is the 827. The true focus of a concave mirror is 


true focus of a point equally distant from the centre and the 
^niirorT surface of the sphere of which the mirror is a 
portion. 


When will 828. When an object is further from the con- 

the image re- cave surface mirror than its focus, the image will be 

aamcavcTe inverted; but when the object is between the 

upright , and mirror and its focus, the image will be upright, 
when invert- , , . .. ,, , . . 

ei li and grow larger in proportion as the object is 

placed nearer to the focus. 

pe- 829. Concave mirrors have the peculiar prop- 
culiar prop- er ty of forming images in the air. The mirroi 
Concave mir- an( ^ the °^j ectl being concealed behind a screen 
rm-s? or a wall, and the object being strongly illumi 


OPTICS. 


225 


natcd, the ra^i, from the object fall upon the minor, and are 
reflected by it through an opening in the screen or wall, forming 
an image in the air. 

Showmen have availed themselves of this property of concave 
mirrors, in producing the appearance of apparitions, which have 
terrified the young and the ignorant. These images have been pre¬ 
sented with great distinctness and beauty, by raising a fine trans¬ 
parent cloud of blue smoke, by means of a chafing-dish, around the 
focus of a large concave mirror. 

’Vhen is the 830. The image reflected by a concave 

l ™ncav/Zhror mirror is lar g er than the object when the 
larger than the object is placed between the mirror and its 
object? focus. 


What is the de~ 831. This is owing to the convergent prop¬ 
s' of fig. erty of the concave mirror. If the object A 
B be placed between the concave mirror and its 
focus f the rays Fig . 129 . 

A and B from its 
extremities will 
tall divergent on 
the mirror, and, 
on being reflect- / 

ed, become less 
divergent, as ' if 
they proceeded 
from C. To an 
eye placed in that situation, namely, at C, the image will appear 
magnified behind the mirror, at a l since it is seen under a 
larger angle than the object. • 



832. There are three cases to be considered with regard to the 
effects of concave mirrors : 

1. When the object is placed between the mirror and the princi 
pal focus. 

2. When it is situated between its centre of concavity and that 
focus. 

3. When it is more remote than the centre of concavity. 

1st. In the first case, the rays of light diverging after reflection 
but in a less degree than before such reflection took place, the im 






NATURAL PHILOSOPHY. 


9T6 

age will be larger than the object and appear at a greater or 
(paajler distance from tlie surface oi the mirror, and behind it. The 
image in this case will be erect. 

2d. When the object is between the principal focus and the cen¬ 
tre of the mirror, the apparent image will be in front of the mirror, 
and beyond the centre, appearing very distant when the object is 
at or just beyond the focus, and advancing towards it as it recedes 
towards the centre of concavity, where, as will be stated, the im¬ 
age and the object will coincide. During the retreat of the object 
the image will still be inverted, because the rays belonging to each 
visible point will not intersect before they reach the eye. But In 
this case the image becomes less and less distinct, at the same time 
that the visual angle is increasing; so that at the centre, or rather 
a little before, the image becomes confused and imperfect, because 
at this point the object and the image coincide. 

3d. In the cases just considered, the images will appear inverted; 
and in the case where the object is further from the mirror than its 
centre of concavity, the image will be inverted. The more distant 
the object is from the centre, the less will be its image ; but the 
image and object will coincide when the latter is stationed exactly 
at the centre. 

833. The following laws flow from the fundamental law of Catop¬ 
trics, namely, that the angles of incidence and reflection are 
always equal. In estimating these angles, it must be recollected 
that no line is perpendicular to a convex or concave mirror, which 
will not, when sufficiently prolonged, pass through the centre cf the 
sphere of which the mirror is a portion. The truth of these state¬ 
ments may be illustrated by simple drawings ; always recollecting, 
in drawing the figures, to make the angles of incidence and reflec¬ 
tion equal. The whole may also be shown by the simple experi¬ 
ment of placing the flame of a candle in various positions before 
both convex and concave mirrors. [It is recommended that the learner 
be required to draw a figure to represent each of these laws. J 

834. Laws of Reflection from Convex Mirrors. — (1.) Par¬ 
allel rays reflected from a convex surface are made to diverge. 

(2.) Diverging rays reflected from a convex surface are made 
more diverging. 

(3.) When converging rays tend towards the focus of parallel 
rays, they will become parallel when reflected from a convex 
Hurface.^ 

(4.) When converging rays tend to a point nearer the surface 

* For the sake of distinction, the principal focus is called “ the Jbcus 
parallel ravs.”— i\: cM 


OPTICS. 


227 


than the focus, they will converge less when reflected from a 
convex surface. 

(5.) If converging rays tend to a point between the focus and 
the centre, they will diverge as from a point on the other side 
of the centre, further from it than the point towards which they 
converged. 

(6.) If converging rays tend to a point beyond the centre, 
they will diverge as from a point on the contrary side of the 
centre, nearer to it than the point towards which they con¬ 
verged. 

(7.) If converging rays tend to the centre, when reflected 
they will proceed in a direction as if from the centre 

835. Laws of Reflection from Concave Mirrors. — 
(1.) Parallel rays reflected from a concave Pirface are made 
converging. [.See Note to No. 837.] 

(2.) Converging rays falling upon a concave surface are 
made to converge more. 

(3.) Diverging rays falling upon a concave surface, if they 
diverge from the focus of parallel rays, become parallel. 

(4.) If from a point nearer to the surface than that focus, 
they diverge less than before reflection. 

(5.) If from a point between that focus and the centre, they 
converge, after reflection, to some point on the contrary side of 
the centre, and further from the centre than the point from 
which they diverged. 

(6.) If from a point beyond the centre, the reflected rays 
will converge to a point on the contrary side, but nearer to it 
than the point from which they diverged. 

(7.) If from the centre, they will be reflected back to the 
(same point from which they proceeded. 

How are objects 83(3* As a necessary consequence of the laws 
seen from a con- which have now been recited, it may be stated, 
vea. mirror ? First, in regard to convex mirrors, the im¬ 
ages of objects invariably appear beyond the mirror; in other 
wQrds : they are virtual images. Secondly, they are seen u* 


228 


NATURAL PHILOSOPHY. 


their natural position, and, Thirdly , they are smaller thas 
the objects themselves; the further the object is from the mir¬ 
ror, and the less the radius of the mirror, the smaller the image 
will be. If the object be very remote, its image will be in the 
virtual focus of the mirror. 

837. Secondly , in regard to concave mirrors. 

(1.) The image of an object very remote from a concave mir¬ 
ror, as that of the sun, will be in the focus of the mirror, ana 
the image will be extremely small.* 

(2.) Every object which is at a distance from the mirror 
greater than its centre produces an image between this point 
and the focus smaller than the object itself, and in an inverted 
position. 

(3.) If the obiect be at a distance from the mirror equal to 
the length of its radius, then the image will be at an equal dis¬ 
tance from the mirror, and the dimensions of the image will be 
the same as those of the object, but its position will be inverted. 

(4.) If the object be between the focus and the centre of 
curvature, the image will be inverted, and its size will much 
exceed that of the object. 

These four varieties of inverted images, produced by tho 
reflection of the rays of light from concave mirrors, are some¬ 
times called “physical spectra .” 

* This is tho manner in which concave mirrors become burning-glasses 
The rays of the sun fall upon them parallel [.see No. 835], and they are all 
reflected into one point, called the focus, where the light and heat are as 
much greater than the ordinary light and heat of the sun as the area of the 
mirror is greater than the area of the focus. It is related of Archimedes, 
that he employed burning-mirrors, two hundred years before the Christian 
era, tv destroy the besieging navy of Marcellus, the Roman consul, llis 
mirror was, probably, constructed from large numbers of flat pieces. M. 
de Vilette constructed a burning-mirror in which the area of the mirror was 
seventeen thousand times greater than the area of the focus. The heat of tho 
sun was thus increased seventeen thousand times. M. Dufay made a concave 
mirror of plaster of Paris, gilt and burnished, twenty inches in diameter, 
with which he set fire to tinder at the distance of fifty feet. But the most 
remarkable thing of the kind on record is the compound mirror constructed 
by Bulfon. He arranged one hundred and sixty-eight small plane mirrors 
in such a manner as to reflect radiant light and heat to the same focus, liko 
one large concave mirror. With this apparatus he was able to set wood on 
fire at the distance of two hundred and nine feet, to melt lead at a hun 
dred feet, and silver at fifty feet. 


OPTICS. 


229 


The existence and position of these spectra may easily be shown 
experimentally thus : 

Experiment .— Hold a candle opposite to a concave mirror, at the 
distances named in the last four paragraphs respectively. The 
spectrum can, in each case, be received on a white screen, which 
must be placed at the prescribed distance from the mirror. 

Different optical instruments, especially reflecting telescopes, 
exhibit the application of these spectra. 

(5.) If a luminous body, as, for instance, the flame of an 
argand lamp, or a burning coal, be placed in the focus of a con¬ 
cave mirror, no image will be produced, but the whole surface 
of the mirror will be illuminated, because it reflects in parallel 
lines all the rays of light that fall upon it. This may be made 
the subject of an experiment so simple as not to require further 
explanation. 

The reflectois of compound microscopes, magic lanterns and light¬ 
houses, by means of which the light given by the luminous body 
is increased and transmitted in some particular direction that may 
be desir'd, are illustrations of the practical .application of this prin 
oiple. 

(6.) Lastly, place the object between the mirror and the 
focus, and the image of the object will appear behind the mir¬ 
ror. It will not be inverted, but its proportions will be enlarged 
according to the proximity of the object to the focus. It is 
this circumstance that gives to concave mirrors their magnifying 
powers, and, because by collecting the sun’s rays into a focus 
they produce a strong heat, they are called burning-mirrors. 

838. Media, or Mediums, and Refrac- 
m.at is a Me- TI0N *— A Medium,* in Optics, is any sub- 
dmm in Optics? stance, solid or fluid, through which light 
can pass. 

What is refrac- 839. When light passes in an oblique 
tlvn ? direction from one medium into another, it 

is turned or bent from its course, and this is called refrac - 

* The proper plural of this word is media, although mediums is frequently 
need. 


20 


230 


NATURAL PHILOSOPHY. 


turn. The property which causes it is called rej rangy 
bility. 


What is Diop¬ 
trics ? 


What is meant 
by a denser and 
rarer meaium 
in Optics ? 


840. Dioptrics. — That part of the sci¬ 
ence of Optics w’hich treats of refracted light 
k called Dioptrics. 

841. A medium, in Optics, is called dense or 
rare according to its refractive power, and not 
according to its specific gravity. Thus, alcohol, 
and many of the essential oils, although of less 

specific gravity than water, have a greater refracting power, 
and are, therefore, called denser media than water. In the fol¬ 
lowing list, the various substances are enumerated in the order 
if their refractive power, or, in other words, in the order of 
.heir density as media, the last-mentioned being the densest, 
and the first the rarest, namely: air, ether, ice, water, alcohol, 
alum, olive oil, oil of turpentine, amber, quartz, glass, melted 
sulphur, diamond. 

842. There are three fundamental laws of 
fundamental & Dioptrics, on which all its phenomena de- 
laivs of Diop- pend, namely : 

(1.) When light passes from one medium 
to another in a direction perpendicular to the surface, it 
continues on in a straight line, without altering its course. 

(2.) When light passes in an oblique direction, from a 
rarer to a denser medium, it will be turned from its course, 
and proceed through the denser medium less obliquely, and 
in a line nearer to a perpendicular to its surface. 

(3.) When light passes from a denser to a rarer medium 
in an oblique direction, it passes through the rarer medium 
in a more oblique direction, and in a line further from a 
perpendicular to the surface of the denser medium. 

843. In Fig. 130, the line A B represents a 
r ay of light passing from air into water, in a 
perpendicular direction. According to the first 


Explain Fig. 
l30. 


OPTICS. 


231 


law stated above, it will continue on in the 
flame line through the denser medium to E. 

If the ray were to pass upward through the 
denser medium, the water, in the same per¬ 
pendicular direction to the air, by the same 
law it would also continue on in the same 
straight line to A. 

But, if the ray proceed from a rarer to a denser medium, in 
an oblique direction, as from C to B, when it enters the denser 
medium it will not continue on in the same straight line to D, 
but, by the second law, stated above, it will be refracted or bent 
out of its course and proceed in a less oblique direction to F, 
which is nearer the perpendicular ABE than I) is. 

Again, if the ray proceed from the denser medium, the water, 
to the rarer medium, the air, namely, from F to B, instead of 
pursuing its straight course to G, it will be refracted according 
to the third law above stated, and proceed in a more oblique 
direction to C, which is further from the perpendicular E B A 
than G is. The refraction is more or less in all 

tion^is P refrac Cases * n P ro P ort ^ on as ra y s ^ a ^ more or ^ es3 
tion in all cases ? obliquely on the refracting surface. 

844. From what has now been stated with 

When are we m re ar( j to re f rac tion, it will be seen that many 
danger oj rms- ® „ 

taking the depth interesting facts may be explained, ihus, an 

df water , and oar? or a stick, when partly immersed in water, 
appears bent, because we see one part in one 
medium, and thb other in another medium: the part which is in 
the water appears higher than it really is, on account of the 
refraction of the denser medium. For the same reason, when 
we look obliquely upon a body of water it appears more shallow 
than it really is. But, when we look perpendicularly down¬ 
wards, we are liable to no such deception, because there will be 
no refraction. 

845. Let a piece of money be put ioto a cup or a bowl, and the 
cup and the eye be placed‘in such a position that the side of the 
«up will just hide the money from the sight; then, keeping the ey* 


Fig, ISO 
G 







232 


NATURAL PHILOSOPHY. 


directed to the same spot, let the cup be filled with water,— ih% 
money will become distinctly visible. 


Why do we not 


846. The refraction of light prevents our 


seethe sun,moon seeing the heavenly bodies in their real situa- 
andstars, in their tion. 

true places. The light which they send to us is refracted 

in passing through the atmosphere, and we see the sun, the 
stars, &c., in the direction of the refracted ray. In conse¬ 
quence of this atmospheric refraction, the sun sheds his light 
upon us earlier in the morning, and later in the evening, than 
we should otherwise perceive it. And, when the sun is actually 
below the horizon, those rays which would otherwise be dissi¬ 
pated through space are refracted by the atmosphere towards 
the surface of the earth, causing twilight. The greater the 
density of the air, the higher is its refractive power, and, conse¬ 
quently, the longer the duration of twilight 


It is proper, however, here to mention that there is another rea¬ 
son, why we do not see the heavenly bodies in their true situ¬ 
ation. Light, though it moves with great velocity, is about eight 
and a half minutes in its passage from the sun to the earth, so that 
when the rays reach us the sun has quitted the spot he occupied 
on their departure ; yet we see him in the direction of those rays, 
and, consequently, in a situation which he abandoned eight minutes 
and a half before. The refraction of light does not affect the appear¬ 
ance of the heavenly bodies when they are vertical, that is, directly 
over our heads, because the rays then pass vertically, a direction 
incompatible with refraction. 


847. When a ray of light passes from 

. What effect is ,. , , , , . 

produced when one medium to another, and through that 

light suffers two into the first again, if the two refractions be 
tton*? re f inC equal, and in opposite directions, no sen¬ 
sible effect will be produced. 


This explains the reason why the refractive power of flat window- 
glass produces no effect on objects seen through it. The rays suffer 
two refractions, which, being in contrary directions, produce the 
game effect as if no refraction had taken place. 

. , . 848. Lenses. — A Lens is a glass, which. 

What is a Lens? . . ’ ’ 

owing to its peculiar form, causes the rays 


OPTICS. 


233 


light to converge to a focus, or disperses them, according 
to the laws of refraction. 


Explain the dif- 849. There are various kinds of lenses, 

fereni kinds of named according to their focus; but they 
are all to be considered as portions of ths 
internal or external surface of a sphere. 


850. A single 
convex lens has 
one side flat and 
the other convex; 
as A, in Fig. 131. 

851. A single 
concave lens is flat 
I> in Fig. 131. 


Fig. 131. 




a 


on one side and concave on the other, as 


852. A double convex lens is convex on both sides, as 
C, Fig. 131. 

A double concave lens is concave on both sides, as D, 
Fig. 131. 

A meniscus is convex on one side and concave on the 
other, as E, Fig. 131. 

What is the 853. The word meniscus is derived from the 

meaning of a Greek language, and means literally a little 

Meniscus ? m, . , ,. j , 

moon. I his term is applied to a concavo-convex 

lens, from its similarity to a moon in its early appearance. To 

this kind of lens the term periscopic has recently been applied, 

from the Greek language, meaning literally viewing on all sides. 

When the concave and convex sides of periscopic glasses are 

even, or parallel, they act as plane glasses; but when the sides 

are unequal, or not parallel, they will act as concave or convex 

lenses, according as the concavity or the convexity is the greater. 

What is the axis 854. The axis of a lens is a line passing 
■tj a lens] through the centre : thus F G, Fig. 131, is 
the axis cf all the five lenses. 

‘ 20 * 







NATURAL PHILOSOPHY. 


”34 


85d. The peculiar form of the various 
lenses kinds of lenses causes the light which passes 

through them to be refracted from its course 
according to tin laws of Dioptrics. 


It will be remembered that, according to these laws, light, in 
,.assing from a rarer to a denser medium, is refracted towards 
the perpendicular; and, on the contrary, that in passing from a 
denser to a rarer medium it is refracted further 

How must we p rom perpendicular. In order to estimate 
estimate the cj- r r ... 

feet of a lens / the effect of a lens, we must consider the situa¬ 
tion of the perpendicular with respect to the 
surface of the lens. Now, a perpendicular, to any convex or 
concave surface, must always, when prolonged, pass through 
the centre of sphericity; that is, in a lens, the centre of the 
sphere of which the lens is a portion. By an attentive observa¬ 
tion, therefore, of the laws above stated, and of the situation of 
the perpendicular on each side of the lens, it will be found, in 
general , — 


(1.) That convex lenses collect the rays into 
What effect hate f ocus all & magnify objects at a certain dis - 

cave lenses re- tance. 

spective/y? (2.) That concave lenses disperse the rays , 

and diminish objects seen through them. 


What is the fc- 856. The focal distance of a lens is the 
cal distance of distance from the middle of the glass to the 
foeus> This, in a single convex lens, is equal 
to the diameter of the sphere of which the lens is a portion, 
and in a double convex lens is equal to the radius of a 
sphere of which the lens is a portion. 


What rays will 
pass through a 
lens without re¬ 
fraction t 


857. When parallel rays* fall on a con* 
vex lens, those only which fall in the direc¬ 
tion of the axis of the lens are perpendicular 
to its surface, and those only will continue 


* The rays of the sun are considered parallel at the surface of the earth. 
They aie not so in reality, but, on account of the great distance of that 
luminary, their divergency is so small that it is altogetbo. inappreciable. 


optics. 


235 


on in a straight line through the lens. The other rays, 
tailing obliquely, are refracted towards the axis, and will 
meet in a focus. 

858. It is this property of a convex lens 

dp/ e W are Twn- which & ives ifc its P ower as a burning-glass, or 
glasses , or sun-glass. All the parallel rays of the sun 
burning-glasses, which pass through the glass are collected to¬ 
gether in the focus; and, consequently, the heat 
at the focus is to the common heat of the sun as the area of the 
glass is to the area of the focus. Thus, if a lens, four inches in 
diameter, collect the sun’s rays into a focus at the distance of 
twelve inches, the image will not be more than one-tenth of an 
inch in diameter; the surface of this little circle is 1600 times 
’.ess than the surface of the lens, and consequently the heat 
will be 1600 times greater at the focus than at the lens. p 

859. The following effects were produced by a large lens, or burn¬ 
ing-glass, two feet in diameter, made at Leipsic in 1691. Pieces of 
lead and tin were instantly melted ; a plate of iron was soon ren¬ 
dered red-hot, and afterwards fused, or melted; and a burnt brick 
was converted into yellow glass. A double convex lens, three feet 
in diameter, and weighing two hundred and twelve pounds, made by 
Mr. Parker, in England, melted the most refractory substances. 
Cornelian was fused in seventy-five seconds, a crystal pebble in six 
seconds, and a piece of white agate in thirty seconds. This lens 
was presented by the King of England to the Emperor of China. 

860. If a convex lens have its sides ground 

What is a Mul- j own i n t 0 several flat surfaces, it will present 
tip lying-glass f , r 

as many images of an object to the eye as it 

has flat surfaces. It is then called a Multiplying-glass. Thus, 

if cne lighted candle be viewed through a lens having twelve 

flat surfaces, twelve candles will be seen through the lens. The 

principle of the multiplying-glass is the same with that of a 

convex or concave lens. 

861. The following effects result from the laws of refraction 

Facts with regard to Convex Surfaces. — (1.) Parallel rays 
passing out of a rarer iiyto a denser medium, through a convex sur 
lace, will become converging. *, 

(2 Diverging rays will bh made to diverge less, to become par 


236 


NATURAL PHILOSOrKY. 


allel, or to converge, according to the degree of d.^ergenev tefor< 
refiaction, or the convexity of the surface. 

(o.] Converging rays towards the centre of convexity will suflei 
no retraction. 

(4.) Rays converging to a point beyond the centre of convexity 
will be made more converging. 

(5.) Converging rays towards a point nearer the surface than 
the centre of convexity will be made less converging by refraction. 

[When the rays proceed out of a denser into a rarer medium, the 
reverse occurs in each case.] 

862. Facts with regard to Concave Surfaces. — (1.) Parallel 
rays proceeding out of a rarer into a denser medium, through a 
concave surface, are made to diverge. 

(2.) Diverging rays are made to diverge more, to suffer no 
refraction, or to diverge less, according as they proceed from a 
point beyond the centre, from the centre, or between the centre and 
the surface. 

(3.) Uonverging rays are made less converging, parallel, or diverg¬ 
ing, according to their degree of convergency before refraction. 

863. The above eight principles are all the necessary consequence 
of the operation of the three laws mentioned as the fundamental 
laws of Dioptrics. The reason that so many different principles are 
produced by the operation of those laws is, that the perpendiculars 
to a convex or concave surface are constantly varying, so that no 
two are parallel. But in flat surfaces the perpendiculars are paral¬ 
lel ;* and one invariable result is produced by the rays when pass¬ 
ing from a rarer to a denser, or from a denser to a rarer medium, 
having a flat surface. 

[When the rays proceed out of a denser into a rarer medium, the 
reverse takes place in each case.] 


What kinds of 
glasses are used 
in spectacles , 
and for what 
nurpose ? 

What kmds of 
glasses are gen¬ 
erally worn by 
old persons l 
What kind by 
young ? 

eye is too flat, 


864. Double convex, and double on cave 
glasses, or lenses, are used in spectacles, to 
remedy the defects of the eye: the former, 
when by age it becomes too flat, or loses a 
portion of its roundness: the latter, when 
by any other cause it assumes too ] ound a 
form, as in the case of short-sighted (or, as 
they are sometimes called, near-sighted) 
persons. Convex glasses are used when the 
and concave glasses when it is too round. 


These lenses or glasses are generally numbered, by opticians, 
according to their degree of convexity or concavity ; so that, by 
knowing the number that fits the eye, the purchaser can generally 
be accommodated without the trouble of trying many glasses. 




i 


OPTICS. 


237 


8t5 Tiie Eye. — The eyes of all animals are constructed on the 
same principles, with such modifications as are necessary to adapt 
them to the habits of the animal. The knowledge, therefore, of the 
construction of the eye of an animal will give an insight of the con¬ 
struction of the eyes of all. 


866. The eye is composed of a number of 
coats, or coverings, within which are enclosed 
a lens, and certain humors, in the shape and 
performing the office of convex lenses.* 


Of what is 
the eye com¬ 
posed ? 


What are the different 867. The different parts of the eye 
parts of the eye ? are : 


(1.) The Cornea. 

(2.) The Iris. 

(3.) The Pupil. 

(4.) The Aqueous Humor. 
(5.) The Crystalline Lens. 


(6.) The Vitreous Humor. 
(7.) The Retina. 

(8.) The Choroid. 

(9.) The Sclerotica. 

(10.) The Optic Nerve. 


Explain 868 * Fi S* 132 re P resents 
Fig. 132. a front view of the eye, in 

which a a represents the Cornea, or, as 
it is commonly called, the white of the 
eye; e e is the Iris, having a circular 
opening in the centre, called the pupil, 
p, which contracts in a strong light, and 
expands in a faint light, and thus reg¬ 
ulates the quantity which is admitted 
„o the tender parts in the interior 
of the eye. 

Explain 869 ‘ Fi S- 133 rc P- 
Fig. 133. resents a side view of 

the eye, laid open, in which h b 
represents the cornea, e e the iris, 
i d the pupil,/* f the aqueous hu¬ 
mor, g g the crystalline lens, h h 



* The following description of the eye is taken principally from Paxton’s 
Introduction to the Study o 1 Anatomy, edited by Dr. Winslow Lewis, ol this 





NATURAL PHILOSOPHY. 


233 

the vitreous humor, i i i i i the retina, c c the choroid, a a a 
a a the sclerotica, and n the optic nerve. 

Describe the 870. The Cornea forms the anterior portion 
Cornea. the eye. It is set in the sclerotica in the same 
manner as the crystal of a watch is set in the case. Its 
degree of convexity varies in different individuals, and in 
different periods of life. As it covers the pupil and the 
iris, it protects them from injury. Its principal office is to 
cause the light which reaches the eye to converge to the 
axis. Part of the light, however, is reflected by its finely- 
polished surface, and causes the brilliancy of the eye. 

Describe the 871. The Iris is so named from its being 
• of different colors. It is a kind of circular 

curtain, placed in the front of the eye, to regulate the quan¬ 
tity of light passing to the back part of the eye. It has a 
circular opening in the centre, which it involuntarily en¬ 
larges or diminishes. 

872. It is on the color of the iris that 
What causes a the color of the eye depends. Thus a person 
beblack, Uue or ^ said to have black, blue, or hazel eyes 
s;ray,<5fc.l according as the iris reflects those colors 

respectively. 

What is the 873. The Pupil is merely the opening in the 
Pupil ? iris, through which the light passes to the lens 
behind. It is always circular in the human eye, but 
in quadrupeds it is of different shape. W nen the pupil i& 
expanded to its utmost extent, it is capable of admitting ten 
times the quantity of light that it does when most con¬ 
tracted. 

874. In cats, and other animals which arc said 
some animals *° see ' m dark, the power of dilatation and con- 
sf-e in the traction is much greater; it is computed that their 
pupils may receive one hundred times more light 


OPTICS. 


289 


at one time than /it another. That light only which parses the 
pupil can be of use in vision; that which falls on the iris, being 
reflected, returns through the cornea, and exhibits the color of 
the iris. 


When we come from a dark place into a strong light, our eyes 
suffer pain, because the pupil, being expanded, admits a larger quan 
tity of light to rush in, before it has had time to contract. And, 
when we go from a strong light into a faint one, we at first imagine 
ourselves in darkness, because the pupil is then contracted, and does 
not instantly expand. 


Describe the 875. The Aqueous Humor is a fluid as clear 
A>/ueous Hu- as the purest water. In shape it resembles a 
nwr ' meniscus, and, being situated between the cor¬ 

nea and the crystalline lens, it assists in collecting and 
transmitting the rays of light from external objects to that 
lens. 


What is the 876. The ^ r J s ^^ ne I jens a transparent 
Crystalline body, in the form of a double convex lens, 
Lens l placed between the aqueous and the vitreous 
humors. Its office is not only to collect the rays to a focus 
on the retina, but also to increase the intensity of the light 
which is directed to the back part of the eye. 

, . j7 877. The Vitreous Humor (so called from'its 

What is the x 

Vitreous Hu- resemblance to melted glass) is a perfectly 

mor • transparent mass, occupying the globe of the 

eye. Its shape is like a meniscus, the convexity of which 
greatly exceeds the concavity. 

878. In .Fig. 134 the shape of the Fi s- 134 - 

aqueous and vitreous humors and the crys¬ 
tal] ine lens is presented. A is the aqueous 
Humor, which is a meniscus, B the crystal¬ 
line lens, which is a double convex lens, 
and C the vitreous humor, which is aide a 
meniscus, whose concavity has a small nr radius than its c«s> 
vexity. 














$ £0 


NATURAL PHILOSOPHY. 


\ fkot it the 879. The Retina is the seat of vision. The 
Kitin,'. 1 r ays of light, being refracted in their passage by 
the other parts of the eye, are brought to a focus in the 
retina, where an inverted image of the object is represented. 

W ! ha t is the 880. The Choroid is the inner coat or cover- 
Choroid ? ing of the eye. Its outer and inner surface 
is covered with a substance called the pigmenium nigrum 
(or black paint). Its office is, apparently, to absorb the 
rays of light immediately after they have fallen on the retina. 
It is the opinion of some philosophers that it is the choroid, 
and not the retina, which conveys the sensation produced 
by rays of light to the brain. 

Describe the 881. The Sclerotica is the outer coat of the 
Sclerotica. eye. It derives its name from its hardness. 
Its office is to preserve the globular figure of the eye, and 
defend its more delicate internal structure. To the sclero¬ 
tica are attached the muscles which move the eye. It re¬ 
ceives the cornea, which is inserted in it somewhat like a 
watch-glass in its case. It is pierced by the optic nerve, 
which, passing through it, expands over the inner surface 
of the choroid, and thus forms the retina. 


882. The Optic Nerve is the organ which 

Optic Nerve 1 carr * es ^he impressions made by the rays of 
light (whether by the medium of the retina, or 
the choroid) to the brain, and thus produces the sensation 
of sight. 

What optical 888. The eye is a natural camera obscura 
does the eye [ S€e No. 805], and the images of all objects 
~ese?nble ? seeil by the eye are represented on the retina 
in the same manner as the forms of external objects are 
delineated in that instrument. 

Explain 884. Fig. 135 represents only those parts of the eye 
13o. are mos t essential for the explanation of the 


OPTIC® 


243 


Fig. 135. 



phenomenon of vision. The image is formed thus: The rays 
from the object c d, diverging towards the eye, enter the cornea 
c, and cross one another in their passage through the crystalline 
tens' d, by which they are made to converge on the retina, wher° 
they form the inverted image f e. 

How is the 885. The convexity of the crystalline humor is 

convexity of increased or diminished by means of two muscles, 

the crystalline to j g attached. By this means, the focua 

lens altered, . J 

and for what of the rays which pass through it constantly falls 
purpose l on the retina; and an equally distinct image is 
formed, both of distant objects and those which are near. 

How can you 886. Although the image is inverted on the re- 
\heapparent ^ na ’ we see Ejects erect, because all the images 
position of formed on the retina have the same relative posi- 
objects ? tion which the objects themselves have ; and, as the 
rays all cross each other, the eye is directed upwards to receive 
the rays which proceed from the upper part of an object, and 
downwards to receive those which proceed from the lower part. 

, 887. A distinct image is also formed on the re- 

Why do we ° 

not see double tina of each eye ; but, as the optic nerves of the 
with two eyes ? two eyes unite, or cross each other, before they 
reach the brain, the impressions received by the two nerves are 
united, so that only one idea is excited, and objects are seen 
single. Although an object nay be distinctly seen with only 
one eye, it has been calculated that the use of both eyes makes 
a difference '>f about one-twelfth. From the description now 
21 



NATURAL PHILOSOPHY. 


M2 


given of the eye, it may be seen what are the defects wnich arc 
remedied by the use of concave and convex lenses, and how the 
use of these lenses remedies them. 


What defects 888. When the crystalline humor of the eye is 
of the eye are too roun( ^ the rays of light which enter the eye 

SV€Ct(lCl6S , 

signed to converge to a focus before they reach the retina, 
remedy ? and, therefore, the image will not be distinct; and 
when the crystalline humor is too fiat (as is often the case with 


old persons), the rays will not converge on the retina, but tend 
to a point beyond it. A convex glass, by assisting the converg- 
ency of the crystalline lens, brings the rays to a focus on the 
retina, and produces distinct vision. 


889. The eye is also subject to imperfection bj 
For what de- „ , J 

fects of the reason the humors losing their transparency 
eye is there either by age or disease. For these imperfectionr. 
no remedy? nQ g] agses 0 g- er a reme dy, without the aid of surgi¬ 
cal skill. The operation of couching and removing cataracts 
from the eye consists in making a puncture or incision through 
which the diseased part may escape. Its office is then supplied 
by a lens. If, however, the operator, by accident or want of 
skill, permit the vitreous humor to escape, the globe of the eye 
immediately diminishes in size, and total blindness is the inevi 
table result 


What is a 890. ^ s ^ n S^ e microscope consists simply of 
single micro- a convex lens, commonly called a magnifying- 
scope? glass ; in the focus of which the object is placed 
and through which it is viewed. 

891. By means of a microscope the rays of light from an 
object are caused to diverge less; so that when they enter the 
pupil of the eye they fall parallel on the crystalline lens, by 
which they are refracted to a focus on the retina. 


Explain 892. Fig. 136 represents a convex lens, or single 
‘ ‘ microscope, C P. The diverging rays from tbe object 

A B arc refracted in their passage through the lens 0 P, and 


OPTICS. 


243 



made to fall parallel on 
the crystalline lens, by 
which they are refracted 
to a focus on the retina 
RR; and the image is 
thus magnified, because 
the divergent rays are 
collected by the lens and 
carried to the retina. 


fig. 136. 


What glasses 893. Those lenses or microscopes which have the 

have the shortest focus have the greatest magnifying power: 
greatest mag- ° ° # J c r 7 

nifying and those which are the most bulging oi convex 

powers ? have the shortest focus. Lenses are made small 


because a reduction in size is necessary to an increase of curva¬ 
ture. 

What is a 894. A double microscope consists of two 
double micro- convex lenses, by one of w T hich a magnified 
scope l image is formed, and by the other this image 
is carried to the retina of the eye. 


Explain 895. Fig. 137 represents the effect produced by the 
hg. 137. j enses 0 f a double microscope. The rays which diverge 
from the object A B are collected by the lens L M (called the 
object-glass, because it is nearest to the object), and form an 


Fig. 137. 



inverted magnified image at C D. The rays which diverge from 
this image are collected by the lens N 0 (called the eye-glass, 
because it is nearest to the eye), which acts on the principle of 





244 


NATUKAL PHILOSOPHY. 


iho single microscope, and forms a still more magnified image on 
the retina R R. 

What is the 896. -^e s0 ^ ar m ^ crosco P e a microscope 
solar micro - with a mirror attached to it, upon a movable 
scope ? joint, which can be so adjusted as to receive 
the sun’s rays and reflect them upon the object. It con¬ 
sists of a tube, a mirror or looking-glass, and two convex 
lenses. The sun’s rays are reflected by the mirror through 
the tube upon the object, the image of which is thrown upon 
i white screen, placed at a distance to receive it. 

897. The microscope, as above described, is used for viewing 
transparent objects only. When opaque objects are to be viewed, 
a mirror is used to reflect the light on the side of the object; 
the image is then formed by light reflected from the object, 
instead of being transmitted through it. 

898. The magnifying power of a single mi- 

How is the mag- crosc 0 p e j s ascertained by dividing the least 
nijymg power ^ t J a 

of single and distance at which an object can be distinctly 

double micro- geen by the na bed e y C by the focal distance of 

tamed t the l ens * 4 his, m common eyes, is about seven 

inches. Thus, if the focal distance of a lens 
be only £ of an inch, then the diameter of an object will be 
magnified 28 times (because 7 divided by I is the same as 7 
multiplied by 4), and the surface will be magnified 784 times. 

The magnifying power of the compound microscope is found 
m a similar manner, by ascertaining the magnifying power, first 
of one lens, and then of the other. 

The magnifying power of the solar microscope is in propor¬ 
tion as the distance of the image from the object-glass is 
greater than that of the object itself from it. Thus, if the dis¬ 
tance of the object from the object-glass be ^ of an inch, and 
the distance of the image, or picture, on the screen, be ten feet, 
ar 120 inches, the object will be magnified in length 480 tames 
or in surface 2o0,000 times. 


oracs. 


245 


A lens may be caused to magnify or to diminish an object. If the 
object be placed at a distance from the focus of a lens, and the im¬ 
age be formed in or near the focus, the image will be diminished; 
but, if the object be placed near the focus, the image will be mag¬ 
nified. 

What is the Mag - The Magic Lantern is an instrument con¬ 
ic Lantern ? structed on the principle of the solar micro¬ 
scope, but the light is supplied by a lamp instead of the 
sun. 

899. The objects to be viewed by the magic lantern are gener¬ 
ally painted with transparent colors, on glass slides, which are 

Fig. 138. 



received into an opening in the front of the lantern. The light 
from the lamp in the lantern passes through them, and carries 
the pictures painted on the slides through the lenses, by means 
of which a magnified image is thrown upon the wall, on a white 
surface prepared to receive it. 

Fig. 188 represents the magic lantern. The 
Describe Fig. ra y S 0 f light f rom the lamp are received upon 
the concave mirror e , and reflected to the con¬ 
vex lens c, which is called the condensing lens, because it con¬ 
centrates a large quantity of light upon the object painted on 
the slide, inserted at b. The rays from the illuminated object 
at b are carried divergent through the lens a , forming an image 
on the screen at f. The image will increase or diminish in size, 
in proportion to the distance of the screen from the ^ns « 

21 * 
























NATURAL PHILOSOPHY. 


iUfl 


900. Dissolving Views. — The exhibition 
called “ Dissolving Views ” is made by means 
of two magic lanterns of equal power, so as t<? 
throw pictures of the same magnitude in the 
on the screen. By the proper adjustment of 
sliding tubes and shutters, one picture on the screen is made 
brighter while the other becomes fainter, so that the one seems 
to dissolve into the other. In the hands of a skilful artist * 
this is an exhibition of the most pleasing kind. 


tioir are “ Dis¬ 
solving Views ” 
represented / 

same position 


What is a Tel- 
tscope t 


901. Telescopes. — A Telescope is an 
instrument for viewing distant objects, and 
causing them to appear nearer to the eye. 


How are tele- 902. Telescopes are constructed by placing 
scopes construct- lenses of different kinds within tubes that slide 
within each other, thus affording opportunity 
of adjusting the distances between the lenses within. 


903, They are also constructed with mirrors, in addition to 
the lenses, so that, instead of looking directly at an object, the 
eye is directed to a magnified image of the object, reflected 
from a concave mirror. This has given rise to 
How many kinds two distinctions in the kinds of telescopes 
there ? ^ in common use, called respectively the Refract¬ 

ing and the Reflecting Telescope. 


How is the Re- 904. The Refracting Telescope is con- 
il^? n mnZw:l structed with lenses alone, and the eye is 
d? directed toward the object itself. 

905. The Reflecting Telescope is con- 
How does a Re- J , , . . . . , ,. 

fleeting Tele- structed with one or more mirrors, in addi- 


* Mr. John A. Whipple, of this city, has given several exhibitions of 
this kind, with great success. A summer scene seemed to dissolve into the 
same scene in mid-winter ; a daylight view was gradually made to faint 
successively into twilight and moonshine; and many changes of a most in 
teresting Lature showed how pleasing an exhibition might be made by a 
skilful combination of science and art 


OPTICS. 


247 


scope differJrom tion tc the lenses; and the image of the 

a Refracting ? n ^ ° . 

object^renected irom a concave mirror, is 
seen, instead of the object itself. 


906. Each of those kinds of telescope has its respective advan¬ 
tages, but refracting telescopes have been so much improved that 
they have in some degree superseded the reflecting telescopes. 

What is an Among the improvements which have 

Achromatic Tele- been made in the telescope, may be mentioned, 
sc0 P e - as the most important, that peculiar construe* 

tion of the lenses by which they are made to give a pencil of 
white light, entirely colorless. Lenses are generally faulty in 
causing the object to be partly tinged with some color, which is 
imperfectly refracted. The fault has been corrected by employ¬ 
ing a double object-glass, composed of two lenses of different 
refracting power, which will naturally correct each other. The 
telescopes in which these are used are called Achromatic. Com¬ 
mon telescopes have a defect arising from the convexity of the 
object-glass, which, as it ^is increased, has a tendency to tinge 
the edges of the images. To remedy this defect, achromatic 
lenses were formed by the union of a convex lens of crown 
glass with a concave lens of flint glass. Owing to the difference 
of the refracting power of these two kinds of glass, the images 
became free from color and more distinct; and hence the glasses 
which produce them were called Achromatic , that is, free from 
color . 


Lenses are also subject to another imperfection, called spheri¬ 
cal aberration , arising from the different degrees of thickness 
in the centre and edges, which causes the rays that are refracted 
through them respectively, to come to different focuses, on ac¬ 
count of the greater or less refracting power of these parts, con¬ 
sequent on their difference in thickness. To correct this defect, 
tenses have been constructed of gems and crystals, &c., which 
have a higher refractive power than glass, and require less 
sphericity to produce equal effects. 

What is the sim- 908> The sim P lest form of tlie telescope cou 
plest form of the sists of two convex lenses, so combined as to 
telescove ? increase the angle of visiou under which the 


NATURAL PHILOSOPHY. 


248 


object is seen. The lenses are so placed that the distance 
between them may be equal to the sum*pf their focal distances 


Which is the 
Object-glass , and 
which the Eye¬ 
glass, of a tele¬ 
scope ? 


909. The lens nearest to the eye is called 
the Eye-glass, and that at the other extrem¬ 
ity is called the Object-glass. 


910. Objects seen through telescopes of this 

wenthrougiitel construc li on (namely, with two glasses only) 
escopes of the are always inverted, and for this reason this 

simplest con- kind 0 f instrument is principally used for as- 
struction? , . . , . , ,, . . « 

tronomical purposes, in which the inversion oi 

the object is immaterial. Hence, this is also called the Night- 

glass. 


911. The common day telescope, or spy- 
is an instrument of the same sort, with 
the addition of two, or even three or four 
glasses, for the purpose of presenting the object 
upright, increasing the field of vision, and diminishing the aber 
ration caused by the dissipation of the rays. 


What is the dif¬ 
ference between 
a day and a 
night telescope? 


912. Fig. 139 represents a night-glass, oi 
Explain Fig. astronomical telescope. It consists of a tube 
A B C D, containing two glasses, or lenses 
The lens A B, having a longer focus, forms the object-glass; 
the other lens D C is the eye-glass. The rays from a very 


Fiir. isa. 



distant body, as a star, and which may be considered parallel to 
each other, are refracted by the object-glass A B to a focus at 
K. The image is then seen through the eye-glass D C, magni¬ 
fied as many times as the focal length of the eye-glass is con¬ 
tained in the focal length of the object-glass. Thus, if the focal 
length of the eye-glass I) C be contained 100 times in that of 













OPTICS. 


249 


the object-glass A B, the star will be seen magnified 100 times. 
It will be seen, by the figure, that the image is inverted ; for 
the ray M A, after refraction, will be seeD in the direction C 0, 
and the ray N B in the direction D P. 


Explain Fig. 
140 . 


913. Fig. 140 represents a day-glass, or ter¬ 
restrial telescope, commonly called a spy-glass. 
This, likewise, consists of a tube A B H (4, 
containing four lenses, or glasses, namely, A B, C 1), E F, and 
G H. The lens A B is the object-glass, and G H the eye-glass. 
The two additional eye-glasses, E F and C D, are of the same 
size and shape, and placed at equal distances from each other 


Fig. 140. 



in such a manner that the focus of the one meets that of the 
next lens. These two eye-glasses E F and C D are introduced 
for the purpose of collecting the rays proceeding from the in¬ 
verted image M N, into a new upright image, between G H and 
E F ; and the image is then seen through the last eye-glass G H, 
under the angle of vision P 0 Q. 

Opera Glasses are constructed on the prin- 

WAfltf are Op- c - j e ^ re f rac ti n g telescope. They are in 
era Glasses? 1 ° 1 J 

fact, nothing more than two small telescopes, 

united in such a manner that the eye-glasses of each may be 

moved together, so as to be adjusted to the eyes of different 

persons. 

Of what does the 914 ‘ TuE R™CTiNa Tjslkscopk. —The Re- 
Reflecting Tel- fleeting Telescope, in its simplest form, con- 
escupe consist? s i s ted of a concave mirror and a convex 
eye-glass. The mirror throws an image of the object, and the 
«ye-glass views that image under a larger angle of vision. 







NATURAL PHILOSOPHY. 


>J50 

This instrument was subsequently improved by Newton, and 
since him by Cassegrain, Gregory, Hadley, Short, and the 
Herschels. 

915. Fig. 141 represents the Gregorian 
Explain Fig. T e i esc0 pe. It consists of a large tube, con 
taining two concave metallic mirrors, and two 
plano-convex eye-glasses. The rays from a distant object are 
received through the open end of the tube, and proceed from r r 

Fig. 141. 


A 



to r r, at the large mirror A B, which reflects them to a focus 
at y, whence they diverge to the small mirror C, which re¬ 
flects them parallel to the eye-glass F, through a circular aper- 
*ure in the middle of the mirror A B. The eye-glass F col¬ 
lects those reflected rays into a new image at I, and this image 
Is seen magnified through the second eye-glass G. 

It is thus seen that the mirrors bring the object near to the 
eye, and the eye-glasses magnify it. Reflecting telescopes are 
attended with the advantage that they have greater magnifying 
power, and do not so readily decompose the light. It has 
already been stated that the improvements in refractors have 
given them the greater advantage. 

How does the 916. The Cassegrainian telescope differs from 
that which has been described, in having the 
differ from smaller mirror convex. This construction is at- 

the Gregorian t tended with two advantages; first, it is superior 
m distinctness of its images, and. second, it dispenses with the 
uece*sity of so long a tube. 













Ol’TICS. 


2o i 


917. The telescopes of Herschel and of Lord 
llosse dispense with the smaller mirror. This is 
done by a slight inclination of the large mirror, so 
Hersckel and 35 to t ^ irow the i ma ge on one side, where it is viewed 
the Earl of by the eye-glass. The observer sits with his back 
Rossc* towards the object to be viewed. Hcrschel’s gigan. 
tic telescope was erected at Slough, near Windsor, in 1789. The 
diameter of the speculum or mirror was four feet, and the mir¬ 
ror weighed 2118 pounds; its focal distance was forty feet. 


What pecu¬ 
liarities are 
there in the 


918. The telescope of Lord Rosse is the largest that has ever been 
constructed. The diameter of the speculum is six feet, and its focal 
distance fifty-six feet. The diameter of the tube is seven feet, and 
the tube and speculum weigh more than fourteen tons. The cost 
of the instrument was about sixty thousand dollars. 

The telescope lately imported for Harvard University is a refract¬ 
or. It is considered one of the best instruments ever constructed. 

What is 919 - Chromatics. —That part of the science 

Chi omatics ? 0 f Optics which relates to colors is called Chro¬ 
matics. 


OJ johat is 920 . Light is not a simple thing in its 

tight composed 1 nature, but is composed of rays of different 
colors, each of which has different degrees of refrangibility, 
and has also certain peculiarities with regard to reflection 
_ . 921. Some substances reflect some of the 

Of what color 

are bodies rays that fall upon them and absorb the others, 

composed / some a pp ear to reflect all of them and absorb 

none, while others again absorb all and reflect none. Hence, 
bodies in general have no color of themselves, independent 
of light, but every substance appears of th it color which it 
reflects. 

922. White is a due mixture of all colors in 

What are , TT , . . 

white and nice and exact proportion. YV hen a body re- 

oladcl fleets all the rays that fall upon it, it will ap¬ 

pear whit 3 , and the purity of the whiteness depends on the 
perfectness of the reflection. 


NATURAL PHILOSOPHY. 




923. Black is the deprivation of all cokr, and, when a 
body reflects none of the rays that fall upon it, it will 
appear black. 

924. Some bodies reflect two or more colors either partially 
or perfectly, and they therefore present the varied hues which 
we perceive, formed from the mixture of rays of diflerent 
colors.* 

What are the 925. The colors which enter into the composi- 
C hrhtJ ^ on ^&kt, and which possess diflerent degrees 
of refrangibility, are seven in number, namely, 
red, orange, yellow, green, blue, indigo, and violet. 

What is a 926. A Prism is a solid, triangular piece of 
Prism ? highly-polished glass. 

927. A prism which will answer the same purpose as a solid one 
may be made of three pieces of plate glass, about six or eight inches 
long and two or three broad, joined together at their edges, and 
made water-tight by putty. The ends may be fitted to a triangular 
piece of wood, in one of which an aperture is made by which to fill 


* When the eye has become fatigued by gazing intently on any object, 
of a red or of any other color, the retina loses, to some extent, its sensitive¬ 
ness to that color, somewhat in the same manner that the ear is deafened for 
a moment by an overpowering sound. If that object be removed and 
another be presented to the eye, of a different color, into the composition of 
which red enters, the eye, insensible to the red, will perceive the other 
colors, or the compound color which they would form by the omission of the 
red, and the object thus presented would appear of that color. The truth 
of this remark may be easily tested. Fix the eye intently for some timo on 
a red wafer on a sheet of white paper. On removing the wafer, the white 
disk beneath it will transmit all the colors of white ligh' but the eye, 
insensible to the red, will perceive the blue or green colors at the other end 
of the spectrum, and the other spot where the red wafer was will appear 
of a bluish-green, until the retina recovers its sensibility for red light. The 
colors thus substituted by the fatigued eye are called the accidental color. 

The accidental colors of the seven prismatic colors, together with biaok 
and white, are as follows : 


Accidental Cohr 

Red .Bluish Green. 

Orange.Blue. 

Yellow.Indigo. 

Green.'.Violet reddish. 

Indigo.Orange red. 

Violet.Orange yellow. 

Black. .White. 

White. . . Black 












OPTICS. 


0 1 


it with water, and thus to give it the appearance and the refractive 
power of a solid prism. 


What effect 
has a prism 
on the light 
chat passes 
through it? 


928. When light is made to pass through a 
prism, the different-colored rajs are refracted 
or separated, and form an image on a screen or 
wall, in which the colors will be arranged in 
the order just mentioned. 


Explain 929. Fig. 142 represents rays of light passing from 
' the aperture, in a window-shutter A B, through the 
prism P. Instead of continuing in a straight course to E, and 
there forming an image, they will be refracted, in their passag* 
through the prism, and form an image on the screen C D. But 


Fig. 142. A 



as the different-colored rays have different degrees of refrangi- 
bility, those which are refracted the least will fall upon the 
lowest part of the screen, and those which are refracted the most 
will fall upon the highest part. The red rays, therefore, suffer¬ 
ing the smallest degree of refraction, fall on the lowest part of 
the screen, and the remaining colors are arranged in the order 
of their refraction. 

930. It is supposed that the red rays are refracted the least, on 
account of their greater momentum ; and that the blue, indigo and 
violet, are refracted the most, because they have the least momentum. 
The same reason, it is supposed, will account for the red appear¬ 
ance of the sun through a fog, or at rising and setting. The in¬ 
creased quantity of the atmosphere which the oblique rays must 
traverse, and its being loaded with mists and vapors, which are 
usually formed at those times, prevents the other rays from reach¬ 
ing us. 

A similar reason will account for the blue appearance of the sky 

22 














254 


NATURAL PHILOSOPHY. 


As these rays have less momentum, they cannot traverse the atmos* 
phere so readily as the other rays, and they are, therefore, reflected 
hack to our eyes by the atmosphere. If the atmosphere did not 
reflect any rays, the skies would appear perfectly black. 

981. If the colored rays which have been sepa* 
blow can the . . . n ,, , ,, 

racs refract- rated by a prism fall upon a convex lens, tuey 

ed by a prism will converge to a focus, and appear white. Hence 

be reunited? ^ appears that white is not a simple color, but is 

produced by the union of several colors. 

932. The spectrum formed by a glass prism being divided 
in+o 360 parts, it is found that the red occupies 45 of those parts, 
the orange 27, the yellow 48, the green 60, the blue 60, the 
indigo 40, and the Violet 80. By mixing the seven primitive 
colors in these proportions, a white is obtained ; but, on account 
of the impurity of all colors, it will be of a dingy hue. If the 
colors were more clearly and accurately defined, the white thus 
obtained would appear more pure also. An experiment to prove 
what has just been said may be thus performed : Take a circular 
pie'ce of board, or card and divide it into parts by lines drawn 
from the centre to the circumference. Then, having painted the 
seven colors in the proportions above named, cause the board to 
revolve rapidly around a pin or wire at the centre. The board 
will then appear of a white color. From this it is inferred 
that the whiteness of the sun’s light arises from a due mixture 
of all the primary colors. 

933. The colors of all bodies are either the simple colors, as 
refracted by the prism, or such compound colors as arise from a 
mixture of two or more of them. 

, 934. From the experiment of Hr. Wollaston, 

What are the . '■ ’ 

three simple ^ appears that the seven colors formed by the prism 

colors ? m ay be reduced to four, namely, red, green, blue, 
and violet; and that the other colors are produced by combina¬ 
tions of these, but violet is merely a mixture of blue and red 
and green is a mixture of blue and yellow. A better division 
of the simple colors is blue, yellow, and red. 

935. Light is found to possess both heat and chemical ad ion 


or rics. 


255 


-v iatic specieum presents some remarkable phenomena with 
rega^ i*j these qualities: for, while the red rays appear to be tna 
seat Of the maximum of heat, the violet, on the contrary, are the 
apparent seat of the maximum of chemical action. 

936. Light, from whatever source it proceeds, is of the same 
nature, composed of the various-colored rays; and although some 
substances appear differently by candle-light from what they appear 
by day, this result may be supposed to arise from the weakness or 
want of purity in artificial light. 

937. There can be no light without colors , and there can be no colors 
without light. 

938. That the above remarks in relation to the colofs of bodies 
are true, may be proved by the following simple experiment. Place 
a colored body in a dark room, in a ray of light that has been re¬ 
fracted by a prism ; the body, of whatever color it naturally is, will 
appear of the color of the ray in which it is placed; for, since it 
receives no other colored rays, it can reflect no others. 

939. Although bodies, from the arrangement of their particles, 
have a tendency to absorb some rays and reflect others, they are 
not so uniform in their arrangement as to reflect only pure rays of 
one color, and perfectly absorb all others ; it is found, on the con¬ 
trary, that a body reflects in great abundance the rays which deter¬ 
mine its color, and the others in a greater or less degree in propor¬ 
tion as they are nearer or further from its color, in the order of 
refrangibility. Thus, the green leaves of a rose will reflect a few of 
the red rays, which will give them a brown tinge. Deepness of 
color proceeds from a deficiency rather than an abundance of reflect¬ 
ed rays. Thus, if a body reflect only a few of the green rays, it 
will appear of a dark green. The brightness and intensity of a 
color show r s that a great quantity of rays are reflected. That bodies 
sometimes change their color, is owing to some chemical change 
which takes place in the internal arrangement of their parts, 
whereby they lose their tendency to reflect certain colors, and 
acquire the power of reflecting others. 

How is a rain- The rainbow is produced by the re- 

bow produced? fraction of the sun’s rajs in their passage 
through a shower of rain; each drop of which acts as a 
prism in separating the colored raj3 as they pass through it. 

941. This is proved by the following considerations: First, 
a rainbow is never seen except when rain is falling and the sun 
shining at the same time; and that the sun and the bow are 
always in opposite parts of the heavens ; and, secondly, that the 
same appearance may be produced artificially, by means of water 
thrown into the air, when the spectator is placed in a proper 


2 5(5 


ICATUIIAL PHILOSOPHY. 


position, with his back to the sun; and, thirdly, that a similar 
bow is generally produced by the spray which arises from large 
cataracts or waterfalls. The Falls of Niagara afford a beautiful 
exemplification of the truth of this observation. A bow is 
always seen there when the sun is clear and the spectator’s back 
is towards the sun. 

942. As the rainbow is produced by the refraction of the sun s 
rays, and every change of position is attended by a corresponding 
change in the rays that reach the eye, it follows that no two persons 
can see exactly the same rainbow, or, rather, the same appearance 
from the same bow. 

943. Polarization of Light. —The Polarization of Light is a 
change produced on light by the action of certain media, by which it 
exhibits the appearance of having polarity, or poles possessing differ¬ 
ent properties. This property of light was firstjiiscovered by Huygens 
in his investigations of the cause of double refraction, as seen in 
the Iceland crystal. The attention of the scientific world was more 
particularly directed to it by the discoveries of Malus, in 1810. The 
knowledge of this singular property of light has afforded an explan¬ 
ation of several very intricate phenomena in Optics, and has afforded 
corroborating evidence in favor of the undulatory theory ; but the lim¬ 
its of this volume will not allow an extended notice of this singular 
property. 

944. Of the Thermal, Chemical, and other Non-optical Effects 
of Light. — The science of Optics treats particularly of light as the 
medium of vision. But there are other effects of this agent, which, 
although more immediately connected with the science of chemistry, 
deserve to be noticed in this connexion. 

945. The thermal effects of light, that is, its agency in the excita¬ 
tion of heat when it proceeds directly from the sun, are well known. 
But it is not generally known that these effects are extremely un¬ 
equal in the differently c^.ored rays, as they are refracted by the 
prism. It has already been stated that the red rays appear to 
possess the thermal properties in the greatest degree, and that in the 
other rays in the spectrum there is a decrease of thermal power 
towards the violet, where it ceases altogether. But, on the contrary, 
chat the chemical agency is the most powerful in the violet, from 
which it constantly decreases towards the red, where it ceases alto¬ 
gether. Whether these thermal and chemical powers exist in all 
light, from whatever source it is derived, remains yet to be ascer¬ 
tained. The chromatic intensity of the colored spectrum is greatest 
in the yellow, from whence it decreases both ways, terminating 
almost abruptly in the red, and decreasing by almost imperceptible 
shades towards the violet, where it becomes faint, and then wholly 
indistinct. Thus it appears that the greatest heating power resides 
where the chemical power is feeblest, and the greatest chemical 


OPTICS. 


or/ 


power where the heating power is feeblest, and tnat the optical 
power is the strongest between the other two. 

946. The chemical properties of light are shown in this, that the 
light of the sun, and in an inferior degree that of day when the sun 
is hidden from view, is a means of accelerating chemical combina¬ 
tions and decompositions. The following experiment exhibits the 
chemical effects of light: 

Place a mixture of equal parts (by measure} of chlorine and hy¬ 
drogen gas in a glass vessel, and no change will happen so long as 
the vessel be kept in the dark and at an ordinary temperature ; but, 
on exposing it to the daylight, the elements will slowly combine 
and form hydrochloric acid ; if the glass be set in the sun’s rays, 
the union will be accompanied with an instantaneous detonation. 
The report may also be produced by transmitting ordinary daylight 
through violet or blue glass to the mixture, but by interposing a red 
glass between the vessel and the light all combination of the elements 
is prevented 

^ ^ . 947. The chemical effects of light have recently 

meant by Pho- been employed to render permanent the images ob- 
tography, or tained by means of convex lenses. The art of thus 
Heliography? fi x ; n g them is termed Photography, or Heliography. 
These words are Greek derivatives; the former meaning “ writing 
or drawing by means of light,” the latter “ writing or draw¬ 
ing by the aid of the sun” 


. , 948. The mode in which the process is performed 

th tS fPh * s e8sentiall J as follows: The picture, formed by a 
° T h t °~ camera obscura, is received on a plate, the surface of 
ograp y. w hich has been previously prepared so as to make it 
as susceptible as possible of the chemical influence of light. After 
the lapse of a longer or shorter time, the light will have so acted on 
the plate that the various objects the images of which were pro¬ 
jected upon it will appear, with all their gradations of light and 
shade, most exactly depicted in black and white, no color being 
present. This is the process commonly known by the name of 
Daguerreotype, from M. Daguerre, the author of the discovery 
Since his original discovery, he has ascertained that by isolating and 
electrifying the plate it acquires such a sensibility to the chemical 
influence of light that one-tenth of a second is a sufficient time to 
obtain the requisite luminous impression for the formation of the 
picture. 

949. The chemical effects of light are seen in the varied colors of 
the vegetable world. Vegetables which grow in dark places are either 
vhite or of a palish-yellow. The sunny side of fruits is of a richer 
tinge than that which grows in the shade. Persons whose daily 
employment keeps them much within doors are pale, and more or 
less sickly, in consequence of such confinement. 

22* 


258 


NATURAL PHILOSOPHY 


From vhat has now been detailed with regard to the nature, the 
offsets, -nd the importance of light, we may see with what reason 
(■he great epic poet of our language has apostrophized it in the 
ft'oris 

«« Hail, holy Light ! offspring of Ht &ven, first born. 

Bright effluence of bright essence increate ; ” 


and why the author of the “ Seasons ” has in a similar manner 
addressed it in the terms : 


“ Prime cheerer, Light! 
Of all material beings first and best! 

Efflux divine ! Nature’s resplendent robe ! 
Without whose vesting beauty all were wrapt 
In unessential gloom ; and thou, 0 Sun ! 

Soul of surrounding worlds, in whom best seen 
Shines out,thy Maker ! may I sing of thee 1 ” 


950. Electricity. — Electricity is the 
name given to an imponderable agent which 
pervades the material world, and which is 
visible only in its effects. 


What is Elec * 
' •nricity ? 


951. It is exceedingly elastic, susceptible of 
simplest Effects] high degrees of intensity, with a tendency to 
equilibrium unlike that of any other known 
agent. Its simplest exhibition is seen in the form of attraction 
and repulsion. 

952. If a piece of amber, sealing-wax, or smooth glass, perfectly 
clean and dry, be briskly rubbed with a dry woollen cloth, and im¬ 
mediately afterwards held over small and light bodies, such as 

f )ieoes of paper, thread, cork, straw, feathers, or' fragments of gold- 
eaf, strewed upon a table, these bodies will be attracted, and fly 
towards the surface that has been rubbed, and adhere to it for a 
certain time. 

953. The surfaces that have acquired this power of attraction 
are said to be excited; and the substances thus susceptible of being 
excited are called electrics , while those which cannot be excited in a 
similar manner are called non-electrics. 


, 954., The science of Electricity, therefore, 

What are the 

'Metrical divis- divides all substances into two kinds, namely, 
tons of all sub - Electrics , or those substances which can be 
excited, and Non-electrics , or those sub 
stances which cannot be excited. 


ELECTRICITY. 


259 


955. The word Electricity is derived from a Greek word, which 
signifies amber, because this substance was supposed to possess, in 
a remarkable degree, the property of producing the fluid, when ex¬ 
cited or rubbed. .The property itself was first discovered by Thales 
oi Miletu^, one of the seven wise men of Greece. The word is now 
used to express both the fluid itself and the science which treats 
oi it. 


What are the ^56. nature of* electricity is entirely 

•prevailing theo- unknown. Some philosophers consider it a 

ries^ of electric- fl u id. others consider it as two fluids of oppo¬ 
site qualities; and others again deny its materi¬ 
ality, and deem it, like ’attraction, a mere property of matter. 
The theory of Dr. Franklin was, that it is a single fluid, dis¬ 
posed to diffuse itself equally among all substances, and exhib¬ 
iting its peculiar effects only when a body by any means becomes 
possessed of more or less than its proper share. That when any 
substance has more than its natural share it is 'positively elec¬ 
trified, and that when it has less than its natural share it is 


negatively electrified, that positive electricity implies a redun¬ 
dancy, and negative electricity a deficiency, of the fluid. The 
prevalent theory at the present day is that it consists of two 
fluids, bearing the names of positive and negative. 


957. Professor Faraday has proposed a nomenclature of elec¬ 
tricity, which has been adopted in some scientific treatises. From 
the Greek words tirr^v, (electricity, or amber , from which it was 
first produced), and iSog (a way or path), he formed the word elec¬ 
trodes , that is, ways or paths of electricity. The course of positive 
electricity he called the anode (from the Greek avoSog, an ascending 
or entering way), and the course of the negative electricity the 
cathode (from the Greek xu&odog, a descending way, or path of exit). 
The terms positive and negative are, however, more frequently em¬ 
ployed to designate the extremities of the channels through which 
electricity passes. Positive electricity is sometimes expressed by 
the term plus, or its character ; and negative electricity by the 
term minus , or its character —. 


How may elec- 958. Electricity may be excited by sev- 
6 X ~ eral modes —as, 1st, by friction, whence it 
is called Frictional Electricity ; 2dly, by chemical action, 
called, from its discoverers. Galvanic , or Voltaic Electric¬ 
ity ; 3dly, by the action of lu at, whence it is called 


260 


NATURAL PHILOSOPHY. 


Thermo-Electricity ; 4thly, by Magnetism. Frictional 
Electricity forms the subject of that branch of Electricity 
usually treated under the head of Natural Philosophy; 
Electricity excited by chemical action forms the subject 
of Galvanism ; and Electricity produced by the agency 
of heat, or by Magnetism, is usually considered in connec¬ 
tion with the subject of Electro-Magnetism. The intimate 
connection between these several subjects shows how close 
are the links of the chain by which all the departments of 
physical science are united. 


What is meant 
by a Conductor 
and a Non-con¬ 
ductor of elec¬ 
tricity 1 


959. The electric fluid is readily commu¬ 
nicated from one substance to another. Some 
substances, however, will not allow it to pass 
through or over them, while others give it a 
free passage. Those substances through 
which it passes without obstruction are called Conductors , 
while those through which it cannot readily pass are called 
Non-conductors ; and it is found, by experiment, that all 
electrics* are non-conductors , and all non-electrics are 
good conductors of electricity. 


960. The following substances are electrics , or non-conductors 
of electricity; namely, 


Atmospheric air (when dry), 
Glass, 

Diamond, 

All precious stones, 

All gums and resins, 

The oxides of all metals, 
Beeswax, 

Sealing-wax, 

All these substances must be 
cr less conductors. 


Feathers, 

Amber, 

Sulpha*, 

Silk, 

Wool, 

Hair, 

Paper, 

Cotton. 

dry, or they will become mow 


m The terms “electrics” and “non-electrics” have fuller, into disuse. 


ELECTRICITY. 


‘261 


961. The following substances are non-electrics, or conductors 
of electricity; namely, 

All metals, Living animals, 

Charcoal, Vapor, or steam. 


962. The following are imperfect conductors (that is, they 
conduct the electric fluid, but not so readily as the substances 
above mentioned^; namely, 

Water, Common wood, 

Green vegetables, Dead animals 

Damp air, Bone, 

Wet wood, Horn, &c. 

All substances containing moisture. 


When is acim - 963. When a conductor is surrounded on 

uctor said to a n sides by non-conducting substances, it is 
s insulated ? J ° 

said to be insulated. 


964. As glass is a non-conducting substance, any conducting 
hubstance surrounded with glass, or standing on a table or stool 
with glass legs, will be insulated. 

965. As the air is a non-conductor when dry, a substance 
which rests on any non-conducting substance will be insulated, 
unless it communicate with the ground, the floor, a table, &c. 


966. When a communication is made be- 
(fuctor char^eT? ^ween a conductor and an excited surface, 
the electricity from the excited surface is 
immediately conveyed by the conductor to the ground; but, 
if the conductor be insulated, its whole surface will become 
electrified, and it is said to be charged. 

What is the 967. The earth may be considered as the 

frand reservoir principal reservoir of elec tricity; and when a 
f electricity? communication exists, by means of any con¬ 
ducting substance, between a body containing more than its 
aatural share of the fluid and the earth, the body will imme 
Lately lose its redundant quantity, and the fluid will eseape to 


262 


NATURAL PHILOSOPHY. 


the earth. Thus, when a person holds a metallic tube to an 
excited surface, the electricity escapes from the surface 10 the 
tube, and passes from the tube through the person to the floor ; 
and the floor being connected with the earth by conducting sub¬ 
stances, such as the timbers, &c., which support the building, 
the electricity will finally pass off, by a regular succession of 
conducting substances, from the excited surface to the earth. 
But, if the chain of conducting substances be interrupted,— that 
is, if any non-conducting substance occur between the excited 
surface and the course which the fluid takes in its progress to 
the earth,— the conducting substances will be insulated, and be¬ 
come charged with electricity. Thus, if an excited surface be 
connected by a long chain to a metallic tube, and the metallic 
tube be held by a person who is standing on a stool with glass 
legs, or on a cake of sealing-wax, resin, or any other non-con¬ 
ducting substance, the^electricity cannot pass to the ground, and 
the person, the chain and the tube, will all become electrified. 


What is the sim¬ 
plest mode of 
exciting electric- 
ity ? 


968. The simplest mode of exciting elec¬ 
tricity is by friction. 


Thus, if a thick cylinder of sealing-wax, or sulphur, or a 
glass tube, be rubbed with a silk handkerchief, a piece of clean 
flannel, or the fur of a quadruped, the electric fluid will be 
excited, and may be communicated to other substances from the 
electric thus excited. 

Whatever substance is used, it must be perfectly dry. It, 
therefore, a glass tube be used, it should previously be held tc 
the fire, ahd gently warmed, in order to remove all moisture 
from its surface. 


What is meant 969 ’ The electricity excited in glass is 
by Vitreous and called the Vitreous or positive electricity ; 
trkity™ elCC an ^ obtained from sealing-wax, or other 
resinous substances, is called Resinous , or 
negative electricity 


ELECTRICITY. 


2 do 

970. The vitreous and lesinous or, in 

f/Tecis ivAcn a other words, the positive and negative elec- 

body is charged tricities, always accompany each other; for, 
with either kind n , - 

of electricity t “ any surface become positive, the surface 

with which it is rubbed will become nega¬ 
tive, and if any surface be made positive, the nearest con¬ 
ducting surface will become negative; and, if positive 
electricity be communicated to. one side of an electric , (as 
a pane of glass, or a glass vial), the opposite side will be- 
jome negatively electrified, and the plate or the glass if. 
then said to be charged. 

971. When one side of a metallic, or other conductoi 
receives the electric fluid, its whole surface is instantly per¬ 
vaded ; but when an electric is presented to an electrified body 
it becomes electrified in a small spot only. 

What is the 972. When two surfaces oppositely electrified are 
effect when united, their powers are destroyed; and, if their 
oppositely un i° n he made through the human body, it pro- 
electrijied are duces an affection of the nerves, called an electric 
united J shock. 

What is the law of 973 - Similar state3 of electricity repe 
electrical attraction each' other ; and dissimilar states attract 
and repulsion? each other. 

Thus, if two pith-balls, suspended by a silk thread, are both 
positively or both negatively electrified, they will repel each 
other; but if one be positively and the other negatively electri¬ 
fied, they will attract each other. 

What is the 974. The Leyden jar is a glass vessel used 
Leyden jar? f or the purpose of accumulating the electr* 
fluid, procured From excited surfaces. 

Explain 97^. Fig. 143 represents a Leyden jar. 1* 
Fig. 143 ^ a g] ass j ar> coated both on the inside and the 

outside with tin-foil, with a cork, or wooden stopper, through 


264 


NATURAL PHILOSOPHY 


which a metallic rod passes, terminating upwards in a biuss 
knob, and connected by means of a wire, at the other Fig. 143 
end, with the inside coating of the jar. The coating 
extends both on the inside and outside only to within 
two or three inches of the top of the jar. Thus pre¬ 
pared, when an excited surface is applied to the 
brass knob, or connected with it by any conducting 
surface, it parts with its electricity, the fluid enters 
the jar, and the jar is said to be charged. 

When a jar is 976. When the Leyden jar is 

IsThf^ek'tric 6 c ^ ar S e( ^» the 18 contained on the 
iiyi surface of the glass. The coating 

serves only as a conductor to the fluid ; and, as this conductor 
within the glass is insulated, the fluid will remain in the jar until 
a communication be made, by means of some conducting sub 
stance, between the inside and the outside coating of the jar. 
If then a person apply one hand or finger to the brass knob, and 
the other to the outside coating of the jar, a communication will 
be fo v med by means of the brass knob with the inside and out¬ 
side of the jar, and the jar will be discharged. A vial or jai 
that is insulated cannot he charged. 



What is an Elec -- 977. An electrical battery is composed of 

incal Battery t a number of Leyden jars connected together. 


The inner coatings of the jars are connected together by 
chains or metallic bars attached to the brass knobs of each jar; 
and the outer coatings have a similar connection established by 
placing the vials on a sheet of tin-foil. The whole battery may 
then be charged like a single jar. For the sake of convenience 
in discharging the battery, a knob connected with the tin-foil on 
which the jars stand projects from the bottom of the box which 
contains the jars. 


What is tie joint - 9 ?8. The jointed discharger is an instru¬ 

ct discharge? ment used to discharge a jar or battery. 


Explain 
Fig. 244. 


Fig. 144 represents the jointed discharger. It 
consists of two rods, generally of brass, terminating 







ELECTRICITY. 


2(>. r ) 


ftt jne end in brass balls, and connected Pi *- 144 

together at the other end by a joint, like 
that of a pair of tongs, allowing them 
to be opened or closed. It is furnished 
with a glass handle, to secure the person 
who holds it from the effects of a shock. 

y 

When opened, one of the balls is made to touch the outside 
coating of the jar, or the knob connected with the bottom of the 
battery, and the other is applied to the knob of the jar or jars. 
A. communication being thus formed between the inside and the 
outside of the jar, a discharge of the fluid will be produced. 



Where must ^79. When a charge of electricity is to be 
a body be sent through any particular substance, the 

talaced, m or- su }) S t ancc mus t form a part of the circuit of 
der to receive 1 J 

a charge of electricity ; that is, it must be placed in such 

electricity ? a manner that the fluid cannot pass from the 
inside to the outside surface of the jar, or battery, without 
passing through the substance in its passage. 

What effect have sharp 98 <>. Metallic rods, with sharp points 
metallic points t silently attract -the electric fluid. 

If the balls be removed from the jointed discharger, and the 
two rods terminate in sharp points, the electricity will pass off 
silently, and produce but little effect. 


How may a 981. A Leyden jar, or a battery, may be silently 
batiery ITs^ discharged by presenting a metallic point, even that 
lently dis- of the finest needle, to the knob; but the point must 
charged l i e brought slowly towards the jar. 


982. It is on this principle that lightning-rods 

cipk°are ‘fight- are constructed. The electric fluid is silently 
rung -rods drawn from the cloud by the sharp points on the 

constructed ? r0( j g} an( j th us p reve nted from suddenly exploding 

on high buildings. 

983. Electricity of one kind or the other is geu- 

What 


is 

meant by 


erally induced in surrounding bodies by the view- 

23 


NATUKA L \ UILOSOPHY. 


5S«$G 


ity of a highly-excited electric. This mode of com- 
Induction ^ municating electricity by approach is styled indue? 
tion. 

984. A body, on approaching another body powerfully elec¬ 
trified, will be thrown into a contrary state of electricity. Thus, 
a feather, brought near to a glass tube excited by friction, will 
be attracted to it; and, therefore, previously to its touching the 
tube, negative electricity must have been induced in it. On the 
contrary, if a feather be brought near to excited sealing-wax , it 
will be attracted, and, consequently, positive electricity must 
have been induced in it before contact. 


What is 985. When electricity is communicated from 
Electricity by one body to another in contact with it, it is 
Transfer ) ca ]] e( j electricity by transfer. 


What is an 986. qq ie e i ec t r ical machine is a machine 
Electrical 

Machine, and constructed for the purpose of accumulating or 
on whatprin- co n ec ting electricity, and transferring it to other 

Is 25 2 1 C071- 

structed? substances;. 

987. Electrical Machines are made in various forms, but all 


on the same principle, namely, the attraction of metallic points. 
The electricity is excited by the friction of silk on a glass sur¬ 
face, assisted by a mixture or preparation called an amalgam, 
composed of mercury, tin, and zinc. That recommended by 
hnger is made by melting together one ounce of tin and two 
mces of zinc, which are to be mixed, while fluid, with six 


unces of mercury, and agitated in an iron or thick wooden box, 
.ntil cold. It is then to be reduced to a very fine powder in a 
.aortar, and mixed with a sufficient quantity cf lard to form it 


mto a paste. 


The glass surface is made either in the form of a cylinder or 
a circular plate, and the machine is called a cylinder or a plata 
machine, according as it is made with a cylinder or with a plate 
Explain 988. Fig, 145 represents a plate electrical ma- 
tig. 145. chine. A 1) is the stand of the machine, L L L L 


KLECTItICIfY. 


an the four glass legs, or posts, which support and insulate the 
parts of the machine. P is the glass plate (which in some ma¬ 
chines is a hollow cylinder) from wh ; ch the electricity is excited, 
and II is the handle by which the plate (or cylinder) is turned. 
R is a leather cushion, or rubber, held closely to both sides of 
the glass plate by a brass clasp, supported by the post G L, 
which is called the rubber-post. S is a silk bag, embraced by 
the same clasp that holds the leather cushion or rubber; and it 
is connected by strings S S S attached to its three other corners, 
and to the legs L L and the fork F of the prime conductor. 0 
is the prime conductor, terminating at one end with a movable 



brass ball. B, and at the other by the fork F, which has one 
prong on each side of the glass plate. On each prong of tho 
fork there are several sharp points projecting towards the plate, 
to collect the electricity as it is generated by the friction of the 
plate against the rubber. V is a chain or wire, attached to the 
brass ball on the rubber-post, and resting on the table or the 
floor, designed to convey the fluid from the ground to the plate 
When negative electricity is to be obtained, this chain is re 
moved from the rubber-post and attached to the prime conductor 
and the electricity is to be gathered from the ball on the rubber 
post. 

Explain the 989 . Operation of the Machine. — By turning 
operation of the handle H, the glass plate is pressed by the rub- 


















NATURAL PHILOSOPHY. 


”68 

tht Electr*' ber. The friction of the rubber against the glass 
al Machine. pj a j e ^ or cylinder) produces a transfer of the elec¬ 
tric fluid from the rubber to the plate; that is, the cushion be¬ 
comes negatively and the glass positively electrified. The fluid 
which thus adheres to the glass, is carried round by the revolu¬ 
tion of the cylinder; and, its escape being prevented by the silk 
Dag, or flap, which covers the plate (or cylinder) until it comes 
to the immediate vicinity of the metallic points on the fork F, 
it is attracted by the points, and carried by them to the prime 
conductor. Positive electricity is thus accumulated on the prime 
conductor, while the conductor on the rubber-post, being deprived 
of this electricity, is negatively electrified. The fluid may then 
be collected by a Leyden jar from the prime conductor, or con¬ 
veyed, by means of a chain attached to the prime conductor, to 
any substance which to be electrified. If both of the conduc¬ 
tors bo insulated, but a small portion of the electric fluid can be 
excited; for this reason, the chain must in all cases be attached 
to the rubber-post , when positive electricity is required, and to 
the prime conductor when negative electricity is wanted. 

What is an 990. On the prime conductor is placed an 
Elect ram- Electrometer, or measurer of electricity. It is 
ivhat a ^Hnd' ma( * e in variou3 forms, but always on the prin- 

ple is it con • ciple that similar states of electricity repel each 
Uructed ? 

"^Jt sometimes consists of a single pith-ball, attached to a light 
rod in the manner of a pendulum, and behind is a graduated arc, 
or circle, to measure the repulsive force by degrees. Sometimes 
it is more simply made (as in the figure), consisting of a wooden 
ball mounted on a metallic stick, or wire, having two pith-balls, 
suspended by silk, hair, or linen threads. When the machine 
is worked, the pith-balls, being both similarly electrified, repel 
each other; and this caus js them to fly apart, as is represented 
in the figure; and they will continue elevated until the electric¬ 
ity is drawn off. But, if an uninsulated conducting substance 
touch the primp aonductor, the pith-balls will fall. The height 


ELECTRICITY. 


20^ 


tc which the balls rise, and the quickness with which they ar« 
elevated, afford some test of the power of the machine. This 
simple apparatus may be attached to any body the electricity 
of which we wish to measure. 

The balls of the electrometer, when elevated, are attracted by 
any resinous substance, and repelled by any vitreous substance 
that has been previously excited by friction. 

991. If an electric, or a non-conductor, be presented to the prime 
conductor, when charged, it will produce no effect on the balls; 
but if a non-electric, or any conducting substance, be presented 
to the conductor, the balls of the electrometer will fall. This 
shows that the conductor has parted with its electricity, and 
that the fluid has passed off to the earth through the substance, 
and the hand of the person presenting it. 

Describe 992. An Electroscope is an instrument, of more 

Bennett's delicate construction, to detect the presence of 
Electroscope, electricity. The most sensitive of this kind of 
apparatus is that called Bennett’s Gold-leaf Electroscope, im¬ 
proved by Singer. It consists of two strips of gold-leaf suspended 
under a glass covering, which completely insulates them. Strip? 
of tin-foil are attached to the sides of the glass, opposite the 
gold-leaf, and when the strips of gold-leaf diverge, they will touch 
the tin-foil, and be discharged. A pointed wire surmounts the 
instrument, by which the electricity of the atmosphere may be 
observed. 

993. An Electrophorus is a simple apparatus by which small 
portions of electricity may be generated by induction. It con¬ 
sists of a disc, or circular cake of resinous substance,* on which 
is laid a smaller circular disc of metal, with a glass handle. Rub 
the resinous disc with hair or the fur of some animal, and the 
metallic disc, being pressed down on the resiu by the finger, 
may then be raised by the glass handle. It will contain a small 
portion of electricity, which may be communicated to the Leyden 
jar, and thus the jar may slowly be charged. 

* A mixture of Shell-lac resin and Venice-turpentine, cast in a tin mould 

23* 


zlO 


NATURAL PHILOSOPHY. 


904. Experiments with the Electrical Machine. — In 
peforming experiments with the Electrical Machine, great car* 
must be taken that all its parts be perfectly dry and clean. 
Moisture and dust, by carrying off the electricity as fast as it is 
generated, prevent successful action. Clear and cold weather 
should be chosen, if possible, as the machine will always perform 
its work better then. 


995. When the machine is turned, if a person touch the prime 
conductor, the fluid passes off through the person to the floor 
without his feeling it. But if he present his finger, his knuckle, 
or any part of the body, near to the conductor, without touching 
it, a spark will pass from the conductor to the knuckle, which 
will produce a sensation similar to the pricking of a pin or 
needle. 

996. If a person stand on a stool with glass legs, or any other 
non-conductor, he will be insulated . If in this situation he 
touch the prime conductor, or a chain connected with it, when 
the machine is worked, sparks may be drawn from any part of 
the body in the same manner as from the prime conductor. 
While the person remains insulated, he experiences no sensation 
from being filled with electricity; or, if a metallic point be pre¬ 
sented to any part of his body, the fluid may be drawn off 
silently, without being perceived. But if he touch a blunt piece 
of metal, or any other conducting substance, or if he step from 
the stool to the floor, he will feel the electric shock ; and the 
shock will vary in force according to the quantity of fluid with 
which he is charged. 


997. The Tissue Figure. Fig. 146 is a 
figure with a dress of fancy paper cut into 
narrow strips. When placed on the prime 
conductor, or, being insulated, is connected 
with it, the strips being all electrified will 
recede and form a sphere around the head. 
On presenting a metallic point to the elec¬ 
trified strips, very singular combinations 
will take place. If the electrometer be 


Fig. 146. 




ICLEOTRIC IT Y . 


271 


removed from the prime conductor, and a tuft of feathers, or 
hair, fastened to a stick or wire, be put in its place, on turning 
the machine the feathers or hair will become electrified, and the 
separate hairs will rise and repel each other. A toy is in this 
way constructed, representing a person under excessive fright. 
On touching the head with the hand, or any conducting substance 
not insulated, the hair will fall. 


How is the 998. The Leyden jar may be charged by pre- 
Leyden jar gen ting it to the prime conductor when the machine 
45 is worked. If the ball of the jar touch the prime 

conductor it will receive the fluid silently; but, if the ball of 
the jar be held at a small distance from the prime conductor, the 
sparks will be seen darting from the prime conductor to the jar 
with considerable noise. 


999. The jar may in like manner be filled with negative elec 
tricity by applying it to the ball on the rubber-post, and con¬ 
necting the chain with the prime conductor. 

1000. If the Leyden jar be charged from the prime conductor 
(that is, with positive electricity), and presented to the pith-balls 
of the electrometer, they will be repelled; but if the jar bd 
charged from the brass ball of the rubber-post (that is, with 
negative electricity), they will be attracted. 

1001. If the ball of the prime conductor be removed, and a 
pointed wire be put in its place, the current of electricity flowing 
from the point when the machine is turned may be perceived by 
placing a lighted lamp before it; the flame will be blown from 
the point; and this will be the case in what part soever of the 
machine the point is placed, whether on the prime conductor or 
tne rubber ; or if the point be held in the hand, and the flame 
placed between it and the machine, thus showing that in all 
cases the fluid is blown from the point. Delicate apparatus 
may be put in motion by the electric fluid when issuing from a 
point. In this way electrical orreries, mills, &c., are constructed 

1002. If the electrometer be removed from the prime con 


272 


NATURAL PHILOSOPHY. 


ductor, and pointed wire be substituted for it, a wire witc 
sharp points bent in the form of an S, balanced on it, will be 
made to revolve rapidly. In a similar manner the motion of 
the sun and the earth around their common centre of gravity, 
together with the motion of the earth and the moon, may be 
represented. This apparatus is sometimes called an Electrical 
Tellurium. It may rest on the prime conductor or upon an insu 
lated stand. 

Describe 1003. A chime of small bells on a stand, 

Fig . 147. Fig. 147, may also be rung by means of 
brass balls suspended' from the revolving wires. 

The principle of this revolution is similar to that 
mentioned in connection with the revolving jet, 

Fig. 98, which is founded on the law that action 
and reaction are equal and in opposite, directions. 

1004. If powdered resin be scattered over dry 
jotton-wool, loosely wrapped on one end of the 
minted discharger, it may be inflamed by the discharge of the 
battery or a Leyden jar. Gunpowder may be substituted for thf 
resin. 

1005. The univei'sal discharger is an instrument fcp 
directing a charge of electricity through any substance 
with certainty and precision. 

Explain 1006. It consists of two sliding rods, A B and ( 
Fig. 148. terminating at the extremities, A and B, with b^an 
balls, and at the other ends which 
rest upon the ivory table or stand 
E, having a fork, to which any 
small substance may be attached. 

The whole is insulated by glass 
legs, or pillars. The rods slide 
through collars, by which means their distance from one anothe 
may be adjusted. 

1007. In using the universal discharger one of the rods oi 
slides must be connected by a chain, or otherwise, with the ou^ 


Fig. 148. 



Fig. 147. 














ELECTRICITY. 


?TH 

Ride, and the other with the inside coating of the jar or battery 
By this means the substance through which the charge is to bo 
Kent is placed within the electric circuit. 

1008. By means of the universal discharger, any small metal¬ 
lic substance may be burnt. The substance must be placed in 
the forks of the slides, and the slides placed within the electric 
circuit, in the manner described in the last paragraph. In the 
same manner, by bringing the forks on the slides into contact 
with a substance placed upon the ivory stand of the discharger, 
such as an egg, a piece of a potato, water, &c., it may be illu 
minated. 

1009. Ether or alcohol may be inflamed by a spark communi 
cated from a person, in the following manner: The person stand 
ing on the insulating stool receives the electric fluid from the 
prime conductor by touching the conductor or any conducting 
substance in contact with it; he then inserts the knuckles o t 
his hand in a small quantity of sulphuric ether, or alcohol, held 
in a shallow metallic cup, by another person, who is not insu¬ 
lated, and the ether or alcohol immediately inflames. In this 
case the fluid passes from the conductor to the person who is 
insulated, and he becomes charged with electricity. As soon 
as he touches the liquid in the cup, the electric fluid, passing from 
him to the spirit, sets it on fire. 

1010. The electrical bells are designed to show the efiectr 
of electrical attraction and repulsion. 

1011. In some sets of instruments, the bells are insulated on a 
separate stand ; but the mode here described is a convenient mode 
of connecting them with the prime conductor. 

1012. They are 
Explain Fig. thus to be ap¬ 
plied : The ball 
B of the prime conductor, with 
its rod, is to be unscrewed, and 
the rod on which the bells are 
suspended is to be screwed in its 


Fig. 149. 

i r— 

J 







^74 


NATURAL l’HILUSOl’liY. 


place. The middle bell is to be connected by a chain with 
the table or the floor. When the machine is turned, the balls 
suspended between the bells will be alternately attracted and 
repelled by the bells, and cause a constant ringing. If the bat¬ 
tery be charged, and connected with the prime conductor, the 
bells will continue to ring until all the fluid from the battery 
has escaped. 

It may be observed, that the fluid from the prime conductor 
passes readily from the two outer bells, which are suspended by 
chains; they, therefore, attract the two balls towards them 
The balls, becoming electrified by contact with the outer bells, 
are repelled by them, and driven to the middle bell, to which 
they communicate their electricity; having parted with their 
electricity, they are repelled by the middle bell, and again 
attracted by the outer ones, and thus a constant ringing is 
maintained. The fluid which is communicated to the middle 
bell, is conducted to the earth by the chain attached to it. 

Explain ivhat 1 ° 1 3 - Spiral Tube. — The passage of tho 
Fig. 150 rep- electric fluid from one conducting substance to 
another, is beautifully exhibited by means of a 
ajlass tube, having a brass ball at each end, and coated in 


Fig. 150. 


KELVIN 


she inside with small pieces of tin-foil, placed at small dis¬ 
tances from each other in a spiral direction, as represented in 
Fig. 150. 

1014. In thesame manner yarious figures, letters and words, may 
be represented, by arranging similar pieces of tin-foil between two 
pieces of flat glass. These experiments appear more brilliant in a 
darkened room. 

„ 7 . „ 1015. The Hydrogen Pistol. — The hydrogen 

' pistol is made in a variety of forms, sometimes 
in the exact form of a pistol and sometimes in 






KLICCI'KICITV. 


the form of a piece 'S ordnance. The form ioi 

in Fig. 151 is a simple and cheap contrivance, 
and is sufficient to explain the manner in 
which the instrument is to be used in any of 
its forms. It is to be filled with hydrogen gas, 
and a cork inserted, fitting tightly. When 
thus prepared, if the insulated knob K be pre¬ 
sented to the prime conductor, it will immediately explode. 


1016. A very convenient and economical 
Expiain Fig. wa y p rocur i n g hydrogen gas for this and 

other experiments, is by means of the hydrogen 
gas generator , as represented in Fig. 152. It consists of a glass 
vessel, with a brass cover, in the centre of which is 
a stop-cock; from the inside of the cover another 
glass vessel is suspended, with its open end down¬ 
wards. Within this a piece of zinc is suspended by 
a wire. The outer vessel contains a mixture of sul¬ 
phuric acid and water, about nine parts of water to 
one of acid. When the cover, to which the inner 
glass is firmly fixed, is placed upon the vessel, the 
acid, acting upon the sine, causes the metal to 
absorb the oxygen of the water, and the hydrogen, 
the other constituent part of the water, being thus 
disengaged, rises in the inner glass, from which it expels the 
water; and when the stop-cock is turned the hydrogen gas may 
be collected in the hydrogen pistol, or any other vessel. In the 
use of hydrogen gas for explosion, it will be necessary to dilute 
the gas with an equal portion of atmospheric air. 


• Fig. 152. 



1017. Electrical Sportsman.— Fig. 153 

Describe the Elec- re p resen t s the Electrical Sportsman, From the 
hicat sportsman. 1 1 

larger ball of a Leyden jar two birds, made of 

pith (a substance procured in large quantities from the corn¬ 
stalk, the whole of which, except the outside, is composed of 
pith', are suspended by a linen thread, silk, or hair. When the 
jar'is charged, the birds wil' rise, as represented in the figure. 










276 


NATURAL PHILOSOPHY. 


on account of the repul¬ 
sion of the fluid in the jar. 

1018. If the jar be then 
placed on the tin-foil of the 
stand, and the smaller ball 
placed within a half inch 
of the end of the gun, a 
discharge will be produced, 
and the birds will fall. 


Kg. 1M 



1019. If images, made of pith, or small 
Explain Fig. pj eces 0 f paper, are placed under the insulated 
stool, and a connection be made between the 
prime conductor and the top of the stool, the images will be 
alternately attracted and repelled; or, in other words, they wil 1 
first rise to the electrified top of the stool, and thus becoming 
themselves electrified, will be repelled, and fall to the ground, 
the floor, or the table; where, parting with their 
electricity, they will again be attracted by the 
stool, thus rising and falling with considerable 
rapidity. In order to conduct this experiment 
successfully, the images, &c., must be placed 
within a short distance of the bottom of the 
stool. 

1020. On the same principle light figures 
may be made to dance when placed between two 
discs, the lower one being placed upon a sliding 
stand with a screw to adjust the distance, and 
the upper one being suspended from the prime conductor, as in 
Fig. 154. 

1021. A hole may be perforated through a quire of paper 
t>^ charging the battery, resting the paper upon the brass bail 
of the battery, and making a communication, by means of the 
jointed discharger, between the ball of one of the jars, and the 
brass ball of the box. The paper, in this case, will be between 
the ball of the battery and the end of the discharger 















ELECTRICITY. 


277 


1022. Gold-leaf may be forced into the poies of glass by 
placing it between two slips of window-glass, pressing the slips 
of glass firmly together, and sending a shock from a battery 
through tiiem. 

If gold-leaf be placed between two cards, and a strong charge 
be passed through them, it will be completely fused. 

1023. When electricity enters at a point, it appears in 
the form of a star; but when it goes out from a point, it 
puts on the appearance of a brush. 

1024. The thunder-house, Fig. 155, is de- 
Describe Fig. s ig ne( j to show the security afforded by light¬ 
ning-rods when lightning strikes a building 
This is done by placing a highly-combustible material in tin 
inside of the house, and passing a 
charge of electricity through it. On 
the floor of the house is a surface of 
tin-foil. The hydrogen pistol, being 
filled with hydrogen gas from the 
gasometer, must be placed on the floor 
of the thunder-house, and connected 
with the wire on the opposite side. 

The house being then put together, a chain must be connected 
with the wire on the side opposite to the lightning-rod, and the 
other end placed in contact either with a single Leyden jar or 
with the battery. When the jar, thus situated, is charged, if a 
connection be formed between the jar and the points of the 
lightning-rod, the fluid will pass off silently, and produce no 
effect. But, if a small brass ball be placed on the points of the 
rod, and a charge of ele^ncity be sent to it from the jar or 
the battery, the gas in the pistol will explode, and throw the 
parts of the house asunder with a loud noise. 

1025. The success of this experiment depends upon the proper con 
ncction of the jar with the lightning-rod and the electrical pistol 
On the side of the house opposite to the lightning-rod there is a 
wire, passing through the side, and terminating on the outside in a 

24 


Fig. 155. 


' 0 

□ 

□ DODO 

□ 

□ 

DU 

OD 

cn 

DD 




00 












rib 


NATURAu WlTLOSUPilY. 


hook V>'hen the house is put together, this wire, ir the insidu 
must touch the tin-foil on the floor of the house. The hydrogen 
pistol must stand on the tin-foil, and its insulated knob, or wire, pro¬ 
jecting from its side, must be connected with the lower end of the 
lightning-rod, extending into the inside of the house. A comrauni 
cation must then be made between the hook on the outside of the 
house and the outside of the jar> or battery. This is conveniently 
done by attaching one end of a chain to the hook, and holding the 
other end in the hand against the side of a charged jar. By pre¬ 
senting the knob of the jar to “he points of the lightning rod no 
effect is produced ; but if a brass ball be placed on the points at P, 
and the knob of the jar be presented to the ball, the explosion will 
take place. If the charged jar be very suddenly presented to the 
points, the explosion may take place; and the jar may be silently 
discharged if it be brought very slowly to the ball. The thunder- 
house is sometimes put together with magnets. 

What is light- 1026 - The phenomena of lightning are 
•ling and thun- caused by the rapid motion o.’ vast quanti¬ 
ties of electric matter. Thunder is the noise 
which accompanies the passage of electricity through the 
air. 


What is sup- 1027. The aurora borealis (or northern 
posed to be the lights) is supposed to be caused by the electric 

“northern lights? P ass i n g through highly-rarefied air; and 

most of the great convulsions of nature, such 
as earthquakes, whirlwinds, hurricanes, water-spouts, &c., are 
generally accompanied by electricity, and often depend upon it 


1028. The electricity which a body manifests by being brought 
near to an excited body, without receiving a spark from it, is 
said to be acquired by induction . When an insulated but un 
electrified conductor is brought near an insulated charged con 
ductor, the end near to the excited conductor assumes a state 
of opposite electricity, while the farther end assumes the same 
kind of electricity,— that is, if the conductor be electrified 
positively, the unelectrified conductor will be negative at the 
nearer end, and positive at the further end, while the middle 
point evinces neither positive nor negative electricity. [Sc* 
No. 993. 


1929. The experiments which have now been described exoi* 


ELECTRICITY. 


270 


f-lifj aU the elementary principles of the science of electricity. 
These experiments may be varied, multiplied, and extended in innu¬ 
merable forms, by an ingenious practical electrician. Among other 
things with which the subject may be made interesting, may bo 
mentioned the following facts, &c. 

1030 A number of feathers, suspended by strings from an insu¬ 
lated conducting substance, will rise and present the appearance of 
a flight of birds. As soon as the substance is discharged, the 
feathers will fall. The experiment may be varied by placing the 
sportsman on the prime conductor, without the use of the Leyden 
jar, to which the birds are attached. 

1031. Instead of the Leyden jar, a plate of common glass (a pane 
of window-glass, for instance) may be coated on both sides with 
tin-foil, leaving the edges bare. A bent wire balanced on the edge 
of the glass, to the ends of which balls may be attached, with an 
image at each end, may be made to represent two persons tilting, cn 
the same principle by which the electrical bells are made to ring. 

1032. Miniature machinery has been constructed, in which the 
power was a wheel, with balls at the ends of the spokes, situated 
within the attractive influence of two larger balls, differently electri¬ 
fied. As the balls on the spokes were attracted by one of the larger 
balls, they changed their electrical state, and were attracted by the 
oth^r, which, in its return, repelled them, and thus the motion being 
given to the wheel was communicated by cranks at the end of the 
axle to the saws above. 

1033. When the hand is presented to the prime conductor, a 
spark is communicated, attended with a slightly painful sensation. 
But, if a pin or a needle be held in the hand with the point towards 
the conductor, neither spark nor pain will be perceived, owing tc 
the attracting (or, perhaps, more properly speaking, the receiving t 
power of the point. 

1034. That square rods are better than round ones to conduct 
electricity silently to the ground, and thus to protect buildings,, 
may be proved by causing each kind of rod to approach the 
prime conductor when charged. It will thus be perceived that, 
while little effect is produced on the pith-balls of the electrom¬ 
eter by the near approach of the round rod, on the approach 
of the square one the balls will immediately fall. The round 
rod, also, will produce an explosion and a spark from the ba 
of the prime conductor, while the square one will draw off the 
fluid silently. 

1035. The effects of pointed conductors upon clouds charged 
with electricity may be familiarly exemplified by suspending a 
*mall fleece of cotton-wool from the prime conductor, and 


280 


NATURAL PHILOSOPHY. 


other smaller fleeces from the upper one, by s nail filaments 
On presenting a point to them they will be repelled, and ah 
drawn together; but, if a blunt conductor approach them, they 
will be attracted. 

1036. From a great variety of facts, it has been ascertained, 
l,hat lightning-rods afford but little security to any part of a 
building beyond twenty feet from them; and that when a rod is 
minted, it loses its conducting power. 



'What are the 1037. The lightning-rods of the most ap- 



* ° with philosophical principles, are composed of 

’’mall square rods, similar to nail-rods. They run over the 


building, and down each of the corners, presenting many 
elevated points in their course. At each of the corners, and on 
the chimneys, the rods should be elevated several feet above the 
building. If the rods are twisted, it will be an improvement, 
as thereby the sharp surfaces presented to collect the fluid will 
point in more varied directions. 

1038. The removal of silk and woollen garments, worn during tno 
day in cold weather, is often accompanied by r. slight noise, resem¬ 
bling that of sparks issuing from a fire. A similar effect is pro¬ 
duced on passing the hand softly over the b*ick of a cat. These 
effects are produced by electricity. 

1039. It may here be remarked, that the terms positive and nega 
tive, are merely relative terms, as applied to the subject of electric 
ity. Thus, a body which is possessed of its natural share of 
electricity, is positive in respect to one that has less, and negative 
in respect to one that has more than its natural share of the fluid, 
oo, also, one that has more than its natural share is positive with 
regard to one that has only its natural share, or less »han its natu 
ral 8hare, and negative in respect to one having a larger share 
than itself. 

1040. The experiments with the spiral tobe connected with Fig 
150 may be beautifully varied by having a collection of such tubes 
placed on a stand ; and ajar coated with small strips, resembling a 
brick wall, presents, when it is charged, a beautiful aypearance ir. 
ihe dark. 

1041. The electric fluid occupies no perceptiblo space of time 
in its passage through its circuit. The rapidity of its motion has 
been estimated as high ;as 288,000 miles in a second of time. It 
always seems to prefer the shortest passage, when the conductor# 


ELECTRICITY. 


281 


arc equally good. Thus, if two, ten, a hundred, or a thousand or 
more persons, join hands, and be made part of the ciieuit of the fluid 
in passing from the inside to the outside of a Leyden jar, they will 
all feel the shock at the same moment of time. But, in its passage, 
the fluid always prefers the best conductors. Thus, if two clouds, 
differently electrified, approach one another, the fluid, in its passage 
irom one cloud to the other, will sometimes take the earth in its 
course, because the air is a bad conductor. 

1042. In thunder-storms the electric fluid sometimes passes from 
the clouds, to the earth, and sometimes from the earth to the clouds, 
and sometimes, as has just been stated, from one cloud to the earth, 
and from the earth to another cloud.* 


WQiat art 1043. It is not safe, during a thunder-storm, to 

comparatively take shelter under a tree, because the tree attracts 

& $afe positions an( *’ ^ human body being a better con- 

during a ductor than the tree, the fluid will leave the tree 
thunder-storm? an d p ass into the body. 

It is also unsafe to hold in the hand edge-tools, or any sharp 
point which will attract the fluid. 

The safest position that can be chosen during a thunder-storm 
is a recumbent posture on a feather bed ,* and in all situations a 
recumbent is safer than an erect position. No danger is to be 
apprehended from lightning when the interval between the flash 
and the noise of the explosion is as much as three or four sec¬ 
onds. This space of time may be conveniently measured by the 
beatings of the pulse, if no time-piece be at hand. 


1044. Lightning-rods were first proposed by Dr. Franklin, to whom 
is also ascribed the honor of the discovery that thunder and light¬ 
ning are the effects of electricity. He raised a kite, constructed of a 
silk handkerchief adjusted to two light strips of cedar, with a 
pointed wire fixed to it; and, fastening the end of the twine to a key, 
and the key, by means of a piece of silk lace, to a post (the silk lace 
serving to insulate the whole apparatus), on the approach of a 


* Am ong the common effects of lightning one of the most familiar is its 
effect On milk. The reason that milk frequently turns sour during the 
prevalence of a thunder-storm, or when the air is surcharged with elec¬ 
tricity, may be thus explained: The air consists of two gases, called oxy¬ 
gen and nitrogen, mixed together, but not chemically combined. Oxygen 
combined with nitrogen produces five deadly poisons ; namely, nitrous 
oxide, nitric oxide, hyponitrous acid, nitrous acid, and nitric acid, accord¬ 
ing to the proportion of each gas which enters into the combination. Th . 
electric fluid causes these gases, which are merely mixed in the air, chem¬ 
ically tu combine and form an acid, which causes the milk to sour 

24 * 


282 


NATURAL PHILOSOPHY. 


thunder-cloud, he was able to collect sparks from the key, to charge 
Leyden jars, and to set fire to spirits. This experiment established 
the identity of lightning and electricity. The experiment was a 
dangtrous one, as was proved in the case of Professor JRichinan, of 
St. Petersburgh, who fell a sacrifice to his zeal for electrical science 
by a stroke oi lightning from his apparatus. 


What are the 1045. Among the most remarkable facts con- 
Electrical nected with the science of electricity, may be men- 
Animals? tioned the power possessed by certain species of 
fishes of giving shocks, similar to those produced by the Leyden 
jar. There are three animals possessed of this power, namely, 
the Torpedo, the Gymnotus Electricus (or Surinam Eel), and 
the Silurus Electricus. But, although it has been ascertained 
that the Torpedo is capable of giving shocks to the animal sys¬ 
tem, similar to those of the Leyden jar, yet he has never been 
made to afford a spark, nor to produce the least effect upon the 
most delicate electrometer. The Gymnotus gives a small but 
perceptible spark. The electrical powers of the Silurus are in¬ 
ferior to those of the Torpedo or the Gymnotus, but still sufficient 
to give a distinct shock to the human system. This power seems 
to have been bestowed upon these animals to enable them to 
secure their prey, and to resist the attacks of their enemies. 
Small fishes, when put into the water where the Gymnotus is 
kept, are generally killed or stunned by the shock, and swallowed 
by the animal when he is hungry. The Gymnotus seems to be 
possessed of a new kind of sense, by which he perceives whether 
the bodies presented to him are conductors or not. The consid¬ 
eration of the electricity developed by the organs of these ani¬ 
mals of the aquatic order, belongs to that department called 
Animal Electricity. 

1046. It will be recollected that the phenomena which have 
now been described with the exception of what has just been 
stated as belonging to animal electricity, belong to the subject 
of frictional electricity. But there are other forms in which 
this subtle agent presents itself, which are yet to be described, 
which show that its operations are not confined to beau*4fu.‘ 


GALVANISM. 




experiments, such as have already been presented, nor to the 
terrific and tremendous effects that we witness in the storm and 
the thunder-gust. Its powerful agency works unseen on the 
intimate relations of the parts and properties of bodies of every 
description, effecting changes in their constitution and character 
so wonderfully minute, thorough arid universal, that it may 
almost be considered as the chief agent of nature, the prime 
minister of Omnipotence, the vicegerent of creative power. 

What is 1047. Galvanism, or Voltaic Electric- 

Galvanism ? ITY . — Galvanism, or Voltaic Electricity, is a 
branch of electricity which derives its name from Galvani, 
who first discovered the principles which form its basis. 

10-48. Dr. Aloysius Galvani was a Professor of Anatomy in Bolog¬ 
na, and made his discoveries about the year 1790. His wife, being 
consumptive, was advised to take, as a nutritive article of diet, some 
soup made of the flesh of frogs. Several of these animals, recently 
skinned for that purpose, were lying on a table in his laboratory, 
near an electrical machine, with which a pupil of the professor was 
amusing himself in trying experiments. While the machine was in 
action, he chanced to touch the bare nerve of the leg of one of the 
frogs with the blade of a knife that he held in his hand, when sud¬ 
denly the whole limb was thrown into violent convulsions. Galvani, 
being informed of the fact, repeated the experiment, and examined 
minutely all the circumstances connected with it. In this way he 
was led to the discovery of the principles which form the basis of 
this science. The science was subsequently extended by the discov 
sues of Professor Volta, of Pavia, who first constructed the galvanic 
y voltaic pile, in the beginning of the present century. 

To produce electricity mechanically (as has been stated under the 
head of frictional electricity), it is necessary to excite an electric or 
non-conducting substance by friction. But galvanic action is pro 
duced by the contact of different conducting substances having a 
chemical action on one another. 


How does gal¬ 
vanism differ 
from friction¬ 
al electricity ? 


1049. Frictional electricity is produced by the 
mechanical action of bodies on one another; but 
galvanism, or galvanic electricity, is produced by 
their chemical action. 


What is the 1050. The motion of the electric fluid, excited 
difference in by galvanic power, differs from that explainec- 
1 frictional and under the head of frictional electricity in its in- 


284 


NATURAL PHILOSOPHY. 


chemical elec- tensity and duration ; for, while the latter exhibit* 
iridty ? itself in sudden and intermitted shocks and explo¬ 

sions, the former continues in a constant and uninterrupted cur¬ 
rent so long as the chemical action continues, and is interrupted 
only by the separation of the substances by which it is produced.* 
^ ^ ^ 1051. The nerves and muscles of animals are 

sensitive to most easily affected by the galvanic fluid; and the 
he galvanic voltaic or galvanic battery possesses the most sur- 
Jiuid? prising powers of chemical decomposition. 


How is the 1052. The galvanic fluid, or influence, is ex- 

galvanic fluid ° . 

excited t cited by the contact of pieces of different metal, 
and sometimes by different pieces of the same metal. 

1053. If a living frog, or a flsh, having a slip of tin-foil on its back, 
be placed upon a piece of zinc, spasms of the muscles will be ex¬ 
cited whenever a communication is made between the zinc and tho 
tin-foil. 

1054. If a person place a piece of one metal, as a half-dollar, 
above his tongue, and a piece of some other metal (as zinc) below 
the tongue, he will perceive a peculiar taste ; and, in the dark, will 


* The different action of gravity on the particles of water while in the 
liquid state, and the same particles in the solid state in the form of ice, has 
been explained in the early pages of this volume. In the one case each 
particle gravitates independently, while in the form of ice they gravitate 
in one mass. The fall of a body of ice would therefore produce more serious 
injury than the fall of the same quantity of water in the liquid form. There 
is a kind of analogy (which, though not sufficient for a philosophical expla¬ 
nation, may serve to give an insight into the difference between the effect* 
produced by frictional electricity and that obtained by chemical means 
between the gravitation of water and ice, respectively, and the motion o : 
frictional and chemical electricity. If the water be dropped in an infinitely 
narrow stream, its effects, although mechanically equal, wT»uld be so gradual 
as to be imperceptible. So, also, if a given portion of electricity be set in 
motion as it were in one mass, and an equal quantity move in an infinitely 
narrow current, there will be a corresponding difference in its apparent 
results. The difference in intensity may perhaps be partially understood by 
this illustration, although a strict analogy may fail to have been made out, 
owing in part to the nature of an imponderable agent. A strict analogy 
cannot exist between the operations of two agents, one of which is pondera¬ 
ble and the other imponderable. But, that there is something like an 
analogy existing in the cases cited, will appear from statements which have 
been made on good authority, namely, that there is a greater quantity of 
electricity developed by the action of a single drop of acid on a very minute 
portion of zinc, than is usually brought ixto action in the darkest cloud that 
rhrouds the horizon. 


GALVANISM. 


28* 


sec a flash of light whenever the outer edges of the metals are m 
contact. 


1055. A faint flash may be made to appear before the eyes by 
putting a slip of tin-foil upon the bulb of one of the eyes, a piece ot 
silver in the mouth, and making a communication between them. 
In these experiments no effect is produced so long as the metals are 
kept apart; but, on bringing them into contact, the effects above 
described are produced. 


What 


It is essential in all cases to have three 


sentiallo pro- elements to produce galvanic action. In the ex- 
duce galvanic periments which have already been mentioned in 
the case of the frogs, the fish, the mouth and the 
eye, the moisture of the animal, or of the mouth, supplies the 
place of the acid, so that the three constituent parts of the circle 
are completed. 


How are the 1057. The conductors of the galvanic fluid, 
galvanism di- like those of frictional electricity, are divided 
vided? into th q perfect and the imperfect. Metallic 

substances, plumbago and charcoal, the mineral acids and 
saline solutions, are perfect conductors. Water, oxydated 
fluids, as the acids, and all the substances that contain these 
fluids, alcohol, ether, sulphur, oils, resins and metallic 
oxydes, are imperfect conductors. 

„ ri .. . r 1058. The acid employed in the galvanic cir 
acid must be cult must always be one that has a strong affinity 
employed in for one of the metals in the circuit. When zinc 
galvanism / em pl 0 j e d, sulphuric acid may form one of the 
three elements, because that acid has a strong affinity for zinc. 
What is a law 1059. A certain quantity of electricity is always 
of chemical developed whenever chemical action takes place 
action / between a fluid and a solid body. This is a gen¬ 

eral law of chemical action ; and, indeed, it has been ascertained 
that there is so intimate a connection between electrical and 
chemical manges, that the chemical action can proceed only to 
a certain extent, unless the electrical equilibrium, which has 
been disturbed, be again restored. Hence, we find that in th*' 


286 


NATURAL PHILOSOJUY. 


simple, as -well as in the compound galvanic circle, the oxydation 
of the zinc proceeds with activity whenever the galvanic circle 
is completed; and that it ceases, or at least takes place very 
slowly, whenever the circuit is interrupted. 


What is neces- 1060. To produce any galvanic action it 
TocxdtevaY- necessary to form what is called a galvanic 
vanic action ? circle , that is, a certain order or succession of 
substances capable t f exciting electricity. 


Of what is the 
simplest gal¬ 
vanic circle 
composed ? 


1061. The simplest galvanic circle is com¬ 
posed of three conductors, one of which must 
be solid, and one fluid ; the third may be either 
solid or fluid. 


What is the 1062. The process usually adopted for obtain- 
Yor obtaining g a i van ^ c electricity is, to place between two 
galvanic elec- plates of different kinds of metal a fluid capable 
tricity? of exerting some chemical action on one of thr 

plates, while it has no action, or a different action, on the other 
A communication is then formed between the two plates. 


Explain 
Fig. 156. 


Fig. 156. 


1063. Fig. 156 represents a 
simple galvanic circle. It con¬ 
sists of a vessel containing a portion of 
diluted sulphuric acid, with a plate of zinc, 

Z, and of copper, C, immersed in it. The 
plates are separated at the bottom, and the 
circle is completed by connecting the two 
plates on the outside of the vessel by means 
of wires. The same effect will be pro¬ 
duced, if, instead of using the wires, the 
metallic plates come into direct contact. 

1064. In the above ar¬ 
il hat are the 

essential parts rangement, there are three 
of a galvanic elements or essential parts, 
namely, the zinc, the copper, 
and the acid The acid, acting chemically Vpon the ssiue. prt< 












GALVANISM. 


^587 


duces an alteration in the electrical btate of the metal. Th« 
sine, communicating its natural share of fhc electrical fluid to 
the acid, becomes negatively electrified. The copper, attracting 
the same fluid from the acid, becomes 'positively electrified. Any 
conducting substance, therefore, placed within the line of com¬ 
munication between the positive and negative points, will re¬ 
ceive the charge thus to be obtained. The arrows in Fig. 156 
show the direction of the current of positive electricity, namely, 
from the zinc to the fluid, from the fluid to the copper, from 
the copper back through the wires to the zinc, passing from 
zinc to copper in the acid, and from copper to zinc out of the 
acid. The substance submitted to the action of the electric cur- 
W/here must a rent must be placed in the line of communication 
substance be between the copper and the zinc. The wire con- 
^afcrtJdby °-al- necte( ^ with the copper is called the positive pole , 
vanic action ? and that connected with the zinc the negative pole , 
and in all cases the substance submitted to galvanic action must 
be placed between the positive and negative poles. 

1065. The electrical effects of a simple galvanic circle, such as 
has now been described, are, in general, too feeble to be perceived, 
except by very delicate tests. The muscles of animals, especially 
those of cold-blooded animals, such as frogs, &c., the tongue, the 
eye, and other sensitive parts of the body, being very easily 
affected, afford examples of the operation of simple galvanio 
circles. In these, although the quantity of electricity set in 
motion is exceedingly small, it is yet sufficient to produce very 
considerable effects; but it produces little or no effect on the 
most delicate electrometer. 

j 1066. The galvanic effects of a simple circle 
vanic "action be may be increased to any degree, by a repetition 
increased ? 0 f the same simple combination. Such repe¬ 
titions constitute compound galvanic circles, and are called 
galvanic piles, or galvanic batteries, according to the mode 
in which they are constructed. 


288 


NATURAL PHILOSOPHY. 


1067. It appears at first view to be a singular fact, that, in a simple 
galvanic circle, composed of zinc, acid and copper, the zinc end 
will always be negative, and the copper end positive; while, in all 
compound galvanic circles composed of the same elements, the zinc 
will be positive, and the copper negative. This apparent difference 
arises from the compound circle being usually terminated by two 
iuperfiuous plates. 

What is the 1068. The voltaic pile consists of alternate 
Voltaic pile ? plates of two different kinds of metal, sepa¬ 
rated by woollen cloth, card, or some similar substance. 

Explain 1069. Fig. 157 represents a voltaic Fig. 157. 

Fig. 157. pile. A voltaic pile may be con¬ 
structed in the following manner: Take a 
number of plates of silver, and the same num¬ 
ber of zinc, and also of woollen cloth,— the cloth 
having been soaked in a solution of sal ammo¬ 
niac in water. With these a pile is to be formed, in the following 
order, namely : a piece of silver, a piece of zinc, a piece of cloth, 
-and thus repeated. These are to be supported by three glass 
rods, placed perpendicularly, with pieces of wood at the top and 
bottom, and the pile will then be complete, and will afford a 
constant current of electric fluid through any conducting sub¬ 
stance. Thus, if one hand be applied to the lower plate, and 
the other to the upper one, a shock will be felt, which will be 
repeated as often as the contact is renewed. 

Instead of silver, copper plates, or plates of other metal, may 
be used in the above arrangement. The arrows in the figure 
show the course of the current of electricity in the arrangement 
of silver, zinc, &c. 

1070. Voltaic piles have been constructed of layers of gold 
and silver paper. The effect of such piles remains undisturbed 
for years. With the assistance of two such piles, an approxi¬ 
mation to 'perpetual motion , in a self-moving clock, has been in¬ 
vented by an Italian philosopher. The motion is produced by 
the attraction and repulsion of the piles exerted on a pith-ball,, 
an the principle of the electrical bells. The top of one of the 






GALVANISM. 




piles was positive, and the bottom negative. The other pile waa 
in an opposite state; namely, the top negative, and the bottom 
positive. 


W\ati$ the 1071. The voltaic, or galvanic battery, is a 
galvanic bat - combination of metallic plates, immersed in 
tery ' pairs in a fluid which exerts a chemical action 

on one of each pair of the plates, and no action, or, at least, 
a different action, on the other. 


What istke 1072. The electricity excited by the battery 
^curreMin the P rocee( ^ s f ro ™ the solid to the fluid, which acts 
galvanic bat- upon it chemically. Thus, in a battery composed 
ter y ■ of zinc, diluted sulphuric acid and copper, the acid 

lets upon the zinc, and not on the copper. The galvanic fluid 
proceeds, therefore, from the zinc to the acid, from the acid to 
the copper, &c. Instead of using two different metals to form 
the galvanic circuit, one metal, in different states, may be em¬ 
ployed ; — the essential principle being, that one of the elements 
shall be more powerfully affected by some chemical agent than 
the other. Thus, if a galvanic pair be made of the same metal, 
one part must be softer than the other (as is the case with cast 
and rolled zinc) ; or a greater amount of surface must be exposed 
to corrosion on one side than on the other; or a more powerful 
chemical agent be used on one side, so that a current will oe 
sent from the part most corroded, through the liquid, to the art 
least corroded, whenever the poles are united, and the circuit 
thereby completed. 

Explain 1073. Fig. 158 represents Fig. 158. 

Fig. 158. a voltaic battery. It con¬ 
sists of a trough made of baked wood, 
wedgewood-ware, or some other non¬ 
conducting substance. It is divided 
into grooves, or partitions, for the re¬ 
ception of the acid, or a saline solution, 
ind tho plates of zinc or copper (or 
other metal) are immersed by pairs in the grooves. The.-f- 





2'JO 


NATURAL PHILOSOPHY. 


pairs of' plates are united by a slip of metai passing from fcne 
one and soldered to the other ; each pair being placed so as 10 
enclose a partition between them, and each cell or groove iD tha 
trough containing a plate of zinc, connected with the copper 
plate of the succeeding cell, and. a copper plate joined with the 
zinc plate of the preceding cell. These pairs must commence 
with copper and terminate with zinc, or commence with zinc and 
terminate with copper. The communication between the first 
and last plates is made by wires, which thus complete the gal¬ 
vanic circuit. The substance to be submitted to galvanic action 
is placed between the points of the two wires. 


How can a 1074. A compound battery of great power is 
compound bat - obtained by uniting a number of these troughs. 
power be ob- l n a similar manner, a battery may be produced 
t.ained? by uniting several piles, making a metallic com¬ 

munication between the last plate of the one and the first plate 
of the next, and so on, taking care that the order of succession 
of the plates in the circuit be preserved inviolate. 


Tsg. 159. 


Describe the 1075 - The Couronm 
Couronne des des tosses , represented in 
lasses. Fig. 159, - g an0 ^ber form 

of the galvanic battery. It consists of 
a number of cups, bowls, or glasses, 
w 'h the zinc and copper plates im¬ 
mersed in them, in the order represent¬ 
ed in the figure; Z indicating the zinc, 
and C the copper plates; the arrows denoting the course, of the 
electric fluid. 



1076. The electric shock from the voltaic battery may be 
received by any number,of persons, by joining hands, having 
previously wetted them, 

Describe Smee's 1077. Smile’s Galvanic Battery is repreientcd 
Battery. in Fig. 160, and affords an instance of a battery 
in its simplest form. It consists of a glass vessel (as a tumbler) 
m which rests the frame that supports the apparatus within 


GALVANISM. 


Two screw-eups rise from the frame, to which 
wires may be attached for the conveyance of 
the electric current in any direction. One of 
the screw-cups communicates with a thin strip 
of platinum, or platinum-foil, which is sus¬ 
pended within the glass vessel between two 
plates of zinc, thus presenting each surface of 
the platinum to a surface of zinc ; and the gal¬ 
vanic action is in proportion to the extent of the opposite sui 
faces of the two metals, and their nearness to each other. The 
other screw-cup is connected with the two zinc plates. The 
screw-cup connected with the platinum is insulated from the 
metallic frame which supports it, by rosewood, and a thumb¬ 
screw confines the zinc plates, so that they can be renewed wb^n 
necessary. The liquid employed for this battery is sulphurs 
acid, or oil of vitriol, diluted with ten parts of water by measure. 
To prevent the action of the acid upon the zinc plates, their sur¬ 
faces are commonly amalgamated, or combined with mercury 
which prevents any chemical action of the acid with the zinc 
until the galvanic circuit is established, when the zinc is imme¬ 
diately attacked by the acid. 

Explain 1078. Fig. 161 represents a series of three pairs 
Fig. 161. of this battery, in which it will be observed that the 


Fig. 161. 



platinum of one is connected with the zinc of the next, and hal 
the terminal wires proceed, consequently, one from a platinum 
plate, and the other from a zinc plate, as in a single pair, 









2€2 


NATURAL PHILOSOPHY. 


Describe the 
sulphate of 
copper bat¬ 
tery by 
Figures 1G2 
and 163 


1078. Sulphate of Copper Battery — Fig 
162 represents a sulphate of copper battery, and 
Fie. 163 a vertical section of the same battery. 

O 

It consists of a double cylinder of copper, C C, 
Fig. 163, with a bottom of the same metal, which 


Fig. 162. 



serves the double purpose of a gal- 
panic plate and a vessel to contain 
the exciting solution. The solu¬ 
tion is contained in the space be¬ 
tween the two copper cylinders. A 
movable cylinder of zinc, Z, is let 
down into the solution whenever 
the battery is to be used. It rests 
on three arms of wood or ivory at 
the top, by means of which it is in¬ 
sulated. Thus suspended in the 
solution, the surfaces of zinc and 
copper, respectively, face each 
other. A screw-cup, N, is at¬ 
tached to the zinc, and anoth¬ 
er, P, to the copper cylinder, 
to receive the wires. When 
a communication is made be¬ 
tween the two cups, electricity 
is excited. The liquid em¬ 
ployed in this battery is a 
solution of sulphate of copper 
(common blue vitriol) in water. A saturated solution is 
first made, and to this solution as much more water is added. 


Fig. 163. 



1079. A pint of water will dissolve about a quarter of a pound ol 
blue vitriol. The solution described above will therefore contain 
about two ounces of the salt to the pint. The addition of alcohol 
in small quantities increases the permanency of the action of the 
solution The zinc cylinder should always betaken out of the solu 
tion when the battery is not in use ; but the solution may remain 
in the battery The battery will keep in good action fer twenty or 
thirty minutes at a time 
































GALVANISM. 


29b 


1980. The sulphate of copper battery, although not so ener¬ 
getic as Smee’s, is found very convenient ir. a large class of 
experiments, and is particularly recommended to those who are 
inexpert in the use of acids; because the sulphate of copper, being 
entirely neutral, will not injure the color nor the texture of 
organic substances. 

Describe the 1081. There is another form of the sulphate of 
protected sul- copper battery, called the Protected Sulphate of 
phate of cop- Copper Battery, which differs from the one described 
l > a erj. k av j n g a porous cell of earthenware, or leather, 
interposed between the zinc and the copper, thus forming two 
cells, in the outer of which sulphate of copper may be used, and 
in the inner one a solution of sulphate of soda (Glauber salt), 
or chloride of sodium (common salt), or even dilute sulphuric 
acid. This battery will continue in use for several days, and it 
is therefore of great use in the electrotype process. 

1082. Grove’s Battery. — This is the most 
battery 6 T ° xe S energetic battery yet known, and is the one 
most generally used for the magnetic telegraph. 
The metals employed are platinum and zinc, and the solutions 
are strong nitric acid in contact with the pla¬ 
tinum, and sulphuric acid diluted with ten or 
twelve parts of water in contact with the zinc. 

This battery must be used with great care, on 
account of the strength of the acids used for 
the solutions, which send out injurious fumes, 
and which are destructive to organic sub¬ 
stances. Fig. 164 represents Grove’s bat¬ 
tery. The containing vessel is glass; within 
this is a thick cylinder of amalgamated zinc, standing on short 
legs, and divided by a longitudinal opening on one side, in order 
to allow the acid to circulate freely. Inside of this is a porous 
cell of unglazed porcelain, containing the nitric acid, and strip 
of platinum. The platinum is supported by a strip of brass 
fixed by a thumb-screw and an insulating piece of ivory to the 

25* 


Fig. 164. 







294 


NATURAL PHILOSOPHY. 


arm proceeding from the zinc cylinder. The amalgamated zinc 
ir not acted upon by the diluted sulphuric acid until the circuit 
of the battery is completed. But, as the nitric acid will filter 
through the porous cell, and act upon the zinc, it is advisable to 
remove the zinc from the acid when the battery is to remain 
inactive. The action of Grove’s battery may be considered as 
three times greater than that of the sulphate of copper battery. 

What are the 1083. The spark from a powerful voltaic bat 

effects of a pow- tery acts upon and inflames gunpowder, char- 

erful voltaic bat- coa y co tton, and other inflammable bodies, fuses 
tery / 

all metals, burns up or disperses diamonds and 
other substances on which heat in other forms produces little or 
no effect. 


1084. The most striking effects of Galvanism on the human 
frame, aft^r death, were exhibited at Glasgow, a few years ago. 
The subject on which the experiments were made was the body of 
the murderer Clydesdale, who was hanged at that city. He had 
Oeen suspended an hour, and the first experiment was made in 
about ten minutes after he was cut down. The galvanic battery 
employed consisted of 270 pairs of four-inch plates. On the appli¬ 
cation of the battery to different parts of the body, every muscle 
was thrown into violent agitation ; the leg was thrown out with 
great violence, breathing commenced, the face exhibited extraordi¬ 
nary grimaces, and the finger seemed to point out the spectators. 
Many persons were obliged to leave the room from terror or sick¬ 
ness ; one gentleman fainted, and some thought that the body had 
really come to life. 


1085. The wires, by which the circuit of the 
battery is completed, are generally covered 
with glass tubes, in order that they may be 
held, or directed to any substance. 

lOj^b^There are three principal circum¬ 
stances in which the electricity produced by 
the galvanic or voltaic battery differs from 
that obtained by the ordinary electrical ma 
chine; namely, 

(1.) The very low degree of intensity of tnat 
produced by the galvanic battery, compared with that obtaine i 


How are the 
hands protected 
when using a 
battery ? 

In what respects 
loes the electric¬ 
ity produced by 
the galvanic bat¬ 
tery differ f rom 
lhat obtained by 
the machine ? 


by the machine 


GAJLVANISM. 


295 


1087 By intensity is here meant something analogous to 
what is implied by density as applied to matter; but in the one 
ease it is a ponderable agent, in the other an imponderable, so 
that a strict analogy cannot be made out between them. The 
term density cannot be applied to any of the imponderable 
agents, light, sound, heat or electricity. We speak of the in¬ 
tensity of light, an intensity of heat, &c. Hence, the word 
intensity is properly applied to electricity, and we speak of its 
tension , instead of its density. 

Which will de - The quantity of electricity obtained by gal- 

i/vtc/jL' , # # 

er quantity of vamc action is much greater than can lie 
electricity , the obtained by the machine; but it flows, as it 

%'2 n nJ$‘n?> Wel ' e ' in narr0W strea . ms - 

Hie action of the electrical machine may be compared to a mighty 
torrent, dashing and exhausting itself in one leap from a precipitous 
height. The galvanic action may be compared to a steady stream, 
supplied by an inexhaustible fountain. In other words, the mo¬ 
mentum of the electricity excited by galvanism is less than that 
from the electrical machine ; but the quantity , as has been stated, 
is greater. 

(2.) The very large quantity of electricity which is set in mo¬ 
tion by the voltaic battery; and, 

(3.) The continuity of the current of voltaic electricity, and 
its perpetual reproduction, even while this current is tending to 
restore the equilibrium. 

1088. Whenever an electrical battery is charged, how great 
soever may be the quantity that it contains, the whole of the 
power is at once expended, as soon as the circuit is completed. 
Its action may be sufficiently energetic while it lasts, but it is 
exerted only for an instant, and, like the destructive operation 
of lightning, can effect during its momentary passage only sud¬ 
den and v : olent changes, which it is beyond human power to 
regulate or control. On the contrary, the voltaic battery con¬ 
tinues, for an indefinite time, to develop and supply vast quan 
tities of electricity, which, far from being lost by returning to 
their source, circulate in a perpetual stream and with undimin- 


NATURAL PHIL CS0PH1 


296 


ished force. The effects of this continued current on the bodie* 
subjected to its action will therefore be more definite, and will 
be constantly accumulating; and their amount, in process of 
time, will be incomparably greater than even those of the ordi¬ 
nary electrical explosion. It is therefore found that changes is 
the composition of bodies are effected by galvanism which cai? 
be accomplished by no other means. The science of galvanism 
therefore, has extended the field and multiplied the means ot 
investigation in the kindred sciences, especially that of Ohem 
istry. 


How are attrac¬ 
tion and repul¬ 
sion manifested 
in the g 
battery J 


1089. A common electrical battery may bo 
charged from a voltaic battery of sufficient 
size ; but a battery constructed of a small num¬ 
ber of pairs, even though the plates are large, 
furnishes no indication of attraction or repul¬ 
sion equal to that which is given by the feeblest degree of 
excitation to a piece of sealing-wax. A galvanic battery con¬ 
sisting of fifty pairs of plates will affect a delicate gold-leaf 
electrometer; an^ yith a series of one thousand pairs, even 
pith balls are made to diverge. 


. , 1090. The effect of the voltaic pile on the 

On what does . . 1 

the effect of the animal body depends chiefly on the number of 

voltaic battery plates that are employed; but the intensity of 

depend l the spark and its chemical agencies increase 

more with the size of the plates than with their number. 


. - 1091. Galvanism explains many facts in 

Mention some of r J 

the familiar ef- common me. 

feds of galvan- Porter, ale, or strong beer, is said to have a 
peculiar taste when drunk from a pewter ves 
scl. The peculiarity of taste is caused by the galvanic circle 
formed by the pewter, the beer, &c., and the moisture of the 
under lip. 

Works of metals the parts of whfcAi are soldered together 
eoon tarnish in the places where the metals are joined. 

Ancient coins composed of a mixture of metal have cruiu* 


GALVANISM. 297 

bled to pieces, while those composed jf pure metal have been 
Uninjured. 

The nails and the copper in sheathing of ships' are soon 
corroded about the place of contact. These are all the effects 
of galvanism. 

There are persons wno profess to be able to find out seams in 
brass and copper vessels by the tongue which the eye cannot 
discover ; and, by the same means, to distinguish the base mix 
tures which abound in gold and silver trinkets. 

1092. From what has now been stated, it will be seen that 
the effects of galvanic action depend on two nrcumstances; 
namely, 1st, the size of the plates employed in the circuit; 
and, 2dly, the number of the pairs constituting a battery. But 
there is a remarkable circumstance to be noticed in this con¬ 
nexion ; namely, that there is one class of facts dependent on 
the extension of the size of the plates, and 
vn what does another on the increase of their number. The 

the 'power oj a ^awer to develop heat and magnetism is de- 
Hittery to pro - 1 1 ° 

auce heat and to pendent on the size of the plates , that is, on the 

affect the animal ex tent of the surface acted upon by the chem- 

7mly U dependT' ical a g ent > while the P ower to decompose 
chemical compounds, and to affect the animal 
system, is affected in a greater ratio by the increase of the 
number of the pairs. 

1093. The name Calorimotor (that is, tki 
What is a Calo - mover 0 f h ea t ) was applied by Dr. Hare, of 
Philadelphia, to a very powerful apparatus which 
he constructed, with large plates, and which he found possessed 
of a very remarkable power in producing heat. Batteries con 
structed for this purpose usually consist of from one to eight 
pairs of plates. They are made in various forms; sometimes 
the sheets of copper and zinc are coiled in concentric spirals, 
sometimes placed side by side; and they may be divided into a 
great number of small plates, provided that all the zinc plates 
aye connected together , and all the copper plates together , and 


NATURAL PHILOSOPHY. 


238 

then ,ho,t the experiments are performed in a channel oj cam* 
munication, opened between the sets of plates, and not between 
pairs, as in the common battery ; for it is immaterial whether 
one large surface be used, or many small ones electrically con¬ 
nected together. The effect of all these arrangements, by which 
the metallic surface of a single pair is augmented, is to increase 
the quantity produced. 

1094. The galvanic or voltaic battery is one of the most valuable 
acquisitions of modern science. It has proved in many instances 
the key by which science has entered into the innermost recesses of 
nature, and discovered the secret of many of her operations. It 
has, in great measure, lifted the hitherto impenetrable veil that has 
concealed the mysterious workings in the material world, and has 
opened a field for investigation and discovery as inviting as it is 
boundless. It has strengthened the sight and enlarged the view of 
the philosopher and the man of science, and given a degree of cer¬ 
tainty to scientific inquiry hitherto known to be unreached, and sup¬ 
posed to be unattainable ; and, if it has not yet satisfied the hopes 
of the alchemist, nor emulated the gold-converting touch of Midas, 
it has shown, almost to demonstration, that science may yet achieve 
wonders beyond the stories of .mythology, and realize the familial 
adage that “ truth is stranger than fiction 

^ . ■ 1095. Magnetism. — Magnetism treats 

netism * * °f ^ lc properties and effects of the magnet, 

or loadstone. 

1096. The term loadstone , or, more properly, leadstone, was ap¬ 
plied to an ore of iron in the lowest state of oxidation, from its 
attractive properties towards iron, and its power of communicating 
its power to other masses of iron. It received the name of Magnet 
from Magnesia, in Asia Minor (now called Guzelhizar), about fif¬ 
teen miles from Ephesus, where its properties were first well known. 
The term magnet is now applied to those substances which, natu¬ 
rally or artificially, are endowed either permanently or temporarily 
with the same attractive power. 

1097. Certain ores of iron are found to be naturally pos¬ 
sessed ol magnetic properties, and are therefore called natural 
or native magnets, or loadstones. Besides iron and some of the 
compounds, nickel, and, perhaps, cobalt, also possess magnetic 
properties. But all conductors of electricity are capable of 
exerting'the magnetic properties of attraction and repulsion 


MAGNETISM. 


299 


while coriveying a current of electricity, as will be shown under 
the head of Electro-Magnetism. 

1098. That part of science which relates to the development of 
magnetism by means of a current of electricity will be noticed un¬ 
der the head of Electro-Magnetism, in which connexion will also 
be mentioned the development of electricity by magnetism, to which 
the term Magneto-Electricity has been applied. 


What are the 
two kinds of 
magnets ? 


1099. There are two kinds of magnets, 
namely, the native or natural magnet, and 
the artificial. 


1100. The native magnet, or loadstone, is an ore of iron, 
found in iron mines, and has the property of attracting 
'ron, and other substances which contain it. 

What is a per- 1101. A permanent artificial magnet is a 
manent magnet ? p j ece 0 f iron to which permanent magnetic 
properties have been communicated. 


\A rack is the 
more useful , the 
permanent 
or the artificial 
magnet ? 


1102. For all purposes of accurate ex¬ 
periment, the artificial is to be preferred to 
the native magnet. 


1103. If a straight bar of soft iron be held in a vertical posi¬ 
tion (or, still better, in a position^lightly inclined to the perpen¬ 
dicular, the lower end deviating to the north), and struck several 
smart blows with a hammer, it will be found to have acquired, 
by this process, all the properties of a magnet; or, in other 
words, it will become an artificial magnet. 

What are the 1104. The properties of a magnet are,— 
properties of a polarity; attraction of unmagnetic iron; at- 
magnet l traction and repulsion of magnetic iron ; the 

power of communicating magnetism to other iron. Besides 
these properties, the magnet has recently been discovered to be 
possessed of electrical properties. These will be considered in 
another connexion. 


What is the po¬ 
int ity of arnag- 
/ 


1105. By the polarity of a magnet is meant 
the property of pointing or turning to the 
north and south poles. The end which points 


300 


NATURAI PHILOSOPHY. 


to the north is called the north pole of the magnet, and the 
other the south pole. 

1106. The attractive power of a magnet is generally stated 
to be greatest at the poles; but the actual poles, or points of 
greatest magnetic intensity, in a steel magnet, are not exactly 
at the ends, but a little witmn them. 


How will a mag- 1107 - When a magnet is supported in 
net move when such a manner as to move freely, it will 
freely suspended l spontaneously 

assume a position directed 

nearly north and south. 

^ 1108. The points to which the poles of a 

magnetic poles? magnet turn are the magnetic poles. These 
do not exactly coincide with the astronomical 
poles of the earth ; but, although the value of the magnetic 
needle has been predicated on the supposition that its polar 
ity is a tendency to point exactly to the north and south 
poles of the earth, the recent discovery of the magnetic 
poles, as the points of attraction, has not depreciated the 
value of the compass, because the variation is known, and 
proper allowances can be made for such variation. 


1109. There are several ways of supporting 

nets supported] a ma g net > so as to enable it to manifest its 
polarity. First , by suspending it, accurately 
balanced, from a string. Secondly , by poising it on a sharp 
point. Thirdly , by attaching it to some buoyant substance, and 
allowing it to float freely on water. 

What is the law -m-m . . r 

of magnetic at- -LUO. Dmerent poles ot magnets attract, 

traction and re- and similar poles repel each other. 
pulsion ? 


m There is here a close analogy between the attractive and repul¬ 
sive powers of the positive and the negative forms of electricity, 
ami the northern and southern polarities of the magnet. The same 
law obtains with regard to both; namely, between like powers here 
is repulsion, between unlike there is attraction 


MAGNETISM. 


301 


1111. A magnet, whether native or artificial attiacts iron or 
riteel which has no magnetic properties; but it both attracts and 
repels those substances when they are magnetic ; that is thy 
north pole of one magnet will attract the south pole of another 
and the south pole of one will attract the north of another, 
but the north pole of the one repels the north pole of the other, 
and the south pole of one repels the south pole of another. 

1112. If either pole of a magnet be brought near any small 
piece of soft iron, it will attract it. Iron filings will also adhere 
in clusters to either pole. 


may 


communicate its 
bodies 


unmagnetized 


To what bod- 1113. A magnet 

ies are the mag- . 

netic properties properties to other 

most easily com- But these properties can be generally con- 
municated? , ,, , , ,, 

veyed to no other substances than iron, 
nickel or cobalt, without the aid of electricity. 

Coulomb has discovered that “ all solid belies are sus¬ 


ceptible of magnetic influence But the u influence ” 
is perceptible only by the nicest tests, and under peculiai 
circumstances. 


What are per- HH- All permanent natural and t judicial 
manent mag- magnets, as well as the bodies on wl ich they 
act, are either iron in its pure state or such 
compounds as contain it. 


What, effect has 1115 ‘ The P owers of a ma S n ‘ are in ' 
the use of a mag- creased by action, and are impaired and 
net on us power l eyen ] on g (P suse> 

V\~h at is a 1H6. When the two poles of a magnet are 
horse-shoe or brought together, so that the magnet resembles 
b magnet ? j n s p a p e a horse-shoe, or the capital letter U, 
it is called a horse-shoe magnet, or a U magnet; and it may 
be made to sustain a considerable weight, by suspending 
substances from a small iron bar, extending from one pole 
26 


m 


NATURAL PHILOSOPHY. 


to the other. This bar is called the keeper A small ad¬ 
dition may be made to the weight every ds*y. 

1117. Soft iron acquires the magnetic power very readily, 
and also loses it as readily; hardened iron or steel acquires 
the property with difficulty, but retains it permanently. 

What follows When a magnet is broken or divided. 

when a mag- each part becomes a perfect magnet, having 
ru.t is divided ? both a nor th and south pole. 

This is a remarkable circumstance, since the central part of a 
magnet appears to possess but little of the magnetic power; 
out, when a magnet is divided in the centre, this very part as¬ 
sumes the magnetic power, and becomes possessed in the one 
part of the north, and in the other of the south polarity. 

1119. The magnetic power of iron or steel appears to reside 
vholly on the surface, and is independent of its mass. 

In ivhat do 1120. In this respect there is a strong resem- 
magnetisrn blance between magnetism and electricity. Elec- 
wstmbleeach tricity, as has already been stated, is wholly con- 
oiherl fined to the surface of bodies. In a few words, 

magnetism and electricity may be said to resemble each other 
in the following particulars : 

(1.) Each consists of two species, namely, the vitreous and 
the resinous (or, the positive and negative) electricities ; and the 
northern or southern (sometimes called the Boreal and the 
Austral) polarity. 

(2.) In both magnetism and electricity, those of the same 
name repel, and those of different names attract each other. 

(3.) The laws of induction in both are similar. 

(4.) The influence, in both cases (as has just been stated) 
resides at the surface , and is wholly independent of their mass. 

What effect H21. Heat weakens, and a great degree of 
has heat m heat destroys the power of a magnet; but the 
« magnet . ma g ne tj c attraction is undiminished by the in¬ 
terposition of any bodies, except iron, steel, &o. 


MAGNETISM. 




f\hat nher 1122. Electricity frequently changes the 
'j'ect U Tpoi aJ - P°^ es a ma § nefc 5 an( i the explosion of a small 
ity of a mag- quantity of gunpowder, on one of the poles. 
net ? produces the same effect. Electricity, also, 

sometimes renders iron and steel magnetic, which were 
not so before the charge was received. 

What is the 1123. The effect produced by two magnets, 
double°rnag- used together, is much more than double that 
net ? of either one used alone. 


What is meant 1124. When a magnet is suspended freely 
by “the dip- f rom Rs centre, the two poles will not lie in 

ping of a mag- , 1 

net, and how the same horizontal direction. This is called 

is it corrected 1 inclination or the dipping of the magnet. 

1125. The tendency of a magnetic needle to dip is corrected, 
in the mariner’s and surveyor’s compasses, by making the south 
ends o-f the needles intended for use in northern latitudes some¬ 
what heavier than the north ends. Compass-needles, intended 
to be employed on long voyages, where great variations of lati¬ 
tude may be expected, are furnished with a small sliding-weight, 
by the adjusting of which the tendency to dip may be counter¬ 
acted. The cause of the dipping of the needle is the superior 
attraction caused by the closer proximity of the pole of the mag¬ 
net to the magnetic pole of the earth. In north latitude, the 
north pole of the needle dips; in south latitude, the south polo. 

In what direc- 1126. The magnet, when suspended, does not 

tion docs a invariably point exactly to the north and south 

magnet point . . . , 

when freely points, but vanes a little towards the east or 

uspended ? the west. This variation differs at different 

■daces, at different seasons, and at different times in the day. 

1127. The variation of the magnetic needle from what has been 

^opposed its true polarity was a phenomenon that lor centuries 

had baffled the science of the philosopher to explain. Recent 

ffscoveries have giv^n a satisfactory explanation of this apparent 


NATURAL PHILOSOPHY. 


804 


anomaly.* The earth has, in fact, four magnetic poles, two of 
which are strong and two are weak. The strongest north pol<? 
is in America, — the weakest, in Asia. The earth itself is consid 
ered as a magnet, or, rather, as composed in part of magnetic 
substances, so that its action at the surface is irregular. The 
variation of the needle from the true geographical meridian ij 
therefore subject to changes more or less irregular, t 

What gift has 1128. The science of Magnetism has rendered 

the science oj j mmense advantages to commerce and navigation, 
Magnetism ° ° 

bestowed on by means of the mariner’s compass. The Mari- 

nacigation ? ner’s Compass consists of a magnetized bar of steel 

Mariner's & ca ^ e( i a needle; having at its centre a cap fitted U 

Compass l it, which is supported on a sharp-pointed pivm 


* The following statement has been made in the National Intelligencer 
on the authority of its London correspondent : 

Mr. Faraday, in a late lecture before the Royal Institution upon th« 
Magnetic Forces, made the following important announcement . 

“ A Herman astronomer has for many years been watching the spots on 
the sun, and daily recording the result. From year to year the groups of 
spots vary. They are sometimes very numerous, sometimes they are few. 
After a while it became evident that the variation in number followed a 
descending scale through five years, and then an ascending scale through 
five subsequent years, — so that the periodicity of the variations became a 
visible fact. 

“ While our German friend was busy with his groups of sun-spots, an 
Englishman was busy with the variations of the magnetic needle, lie, too. 
was a patient recorder of patient observation. On comparing his tabuhu 
results with those of the German astronomer, he found that the variations 
of the magnetic needle corresponded with the variations of the sun-spots,— 
that the years when the groups were at their maximum, the variations of 
the needle were at their maximum, and so on through their series. This 
relation may be coincident merely, or derivative ; if the latter, then do we 
connect astral and terrestrial magnetism, and new reaches of science are 
open to us.” 

f This subject is very ably treated in “ Davis’ Manual of Magnetism” 
(edition of 1847), to which the student is referred, as probably the best 
elementary treatise on the subject that has been published. Mr. Davis is 
one of those scientific and skilful mechanics (of whom there are not a few 
among us) who have, as it were, forced their way into the temple of science 
amid discouragements and difficulties, but have deposited richer gifts on the 
altar than most of those whose contributions were expected. He has 
originated many improvements in this department of science ; and his 
devotion to the subject has probably rendered him as familiar with all the 
peculiar phenomena relating to it as any one in or out of the country. 

Mr-. Davis has been succeeded by two intelligent and skilful young men 
Palmer and Hall, Magnetical Instrument Makers, 5‘2G Washington streo , 
Huston. They are also the agents for the sale of his works, “ The Hook of 
tuc Telegraph.” and “ Medical Electricity.” 


MAUKETISM. 


306 


5xe4 in the base of the instrument. A circular plate, or card, 
the circumference of which is divided into degrees, is attached 
to the needle, and turns with it. On an inner circle of the card 
the thirty-two points of the mariner’s compass are inscribed 


Fig 165. 



1129. The needle is generally placed under the card of a 
mariner’s compass, so that it is out of sight; but small needles, 
used on land, are placed above the card, not attached to it, and 
the card is permanently fixed to the box. 

1130. The compass is generally fitted by two sets of axes to 
an outer box, so that it always retains a horizontal position, 
even when the vessel rolls. When the artificial magnet or needle 
is kept thus freely suspended, so that it may turn north or south, 
the pilot, by looking at its position, can ascertain in what direc¬ 
tion his vessel is proceeding ; and, although the needle varies a 
little from a correct polarity, yet this variation is neither so 
great, nor ro irregular as seriously to impair its use as a guide 
to the vessel in its course over the pathless deep. 

26 * 










KaXUK tL l'HILOSOPH Y 


306 

1131. The invention of the mariner’s ompass is usually 
ascribed to Flavio de Melfi, or Flavio Gioia. a Neapolitan, about 
the year 1302. Some authorities, however, assert that it was 
brought from China by Marco Paolo, a Venetian, in 1260. Tne 
invention is also claimed both by the French and English. 


1132. The value of this discovery may be esti- 
fas t 'f l€ mar _ mated from the consideration that, before the use 
incr's com- of the compass, mariners seldom trusted themselves 
pass been ? ou t gjgj^ 0 f j an( j . they were unable to make 
long or distant voyages, as they had no means to find their way 
back. This discovery enabled them to find a way where all is 
trackless ; to conduct their vessels through the mighty ocean, 
out of the sight of land ; and to prosecute those discoveries, and 
perform those gallant deeds, which have immortalized the names 
of Cook, of La Perouse, Vancouver, Sir Francis Drake, Nelson. 
Parry, Franklin and others. 


Which pole of H33. The north pole of a magnet is more 
Ihemore ** powerful in the northern hemisphere, or north 
powerful ? of the equator, and the south pole in the south¬ 
ern parts of the world. 

1134. When a piece of iron is brought sufficiently near to a 
magnet, it becomes itself a magnet; and bars of iron that have 
stood long in a perpendicular situation are generally found to 
be magnetical. 

„ A . 1135. Artificial magnets are made by apply- 

ficial magnets ing one or more powerful magnets to pieces of 
model soft iron. The end which is touched by the 

north pole becomes the south pole of the new magnet, and 
that touched by the south pole becomes the north pole. The 
magnet which is employed in magnetizing a steel bar loses 
none of its power by being thus employed ; and, as the effect 
i 3 increased when two or more magnets are used, with one 
•nagnet a number of bars may be magnetized, and then com¬ 
bined together: by which means their power may be 


MAGNETISM. 807 

indefinitely increased. Such an apparatus is called a 7tMg- 
netic magazine. 

1136. There are several methods of making artificial magnets. 
One of the most simple and effectual consists in passing a strong 
Horse-shoe magnet over bars of soft iron. 

In making bar (or straight) magnets, the bars must be laid 
lengthwise, on a fiat table, with the marked end of one bar 
against the unmarked end of the next; and in making horse¬ 
shoe magnets, the pieces of steel, previously bent into their 
proper form, must be laid with their ends in contact, so as to 
form a figure like two capital U’s, with their tops joined together, 
thus, Cp; observing that the marked ends come opposite to 
those which are not marked; and then, in either case, a strong 
horse-shoe magnet is to be passed, with moderate pressure, over 
the bars, taking care to let the marked end of this magnet pre¬ 
cede and its unmarked end follow it, and to move it constantly 
over the steel bars, so as to enter or commence the process at a 
mark, and then to proceed to an unmarked end, and enter the 
next bar at its marked end, and so proceed. 

After having thus passed over the bars ten or a dozen times 
im each side, and in the same direction as to the marks, they 
will be converted into tolerably strong and permanent magnets 
But if, after having continued the process for some time, the 
fcxeiting magnet be moved over the bars in a contrary direc¬ 
tion, or if its south pole should be permitted to precede after 
the north pole has been first used, the previously-excited mag¬ 
netism will disappear, and the bars will be found in their original 
state. 

This mode .of making artificial magnets is likely to be wholly 
superseded by the new mode by electrical aid which will be 
noticed in connexion with Electro-magnetism. 

Iloioisamag - 1137. A magnetic magazine may be made by 

vetic maga- taking several horse-shoe magnets of equal size, 
zinc constructed? ... ,, 

and, after having magnetized them, uniting them 

together by means of screws. 


308 


NATURAL PHILOSOPHY. 


1138. A magnetic needle is made by fastening the steel on a 
piece of ooard, arid drawing magnets over it from the centre 
outwards. / 

1139. A horse-shoe magnet should be kept 
horse *shoe** ° arme ^ by a small bar of iron or steel, connect- 
magnet be kept ? ing the two poles. The bar is called “ the 
keeper .” 

interesting experiments may be made by a magnet, even of no 
great power, with steel or iron filings, small needles, pieces of fer¬ 
ruginous substances, and black sand which contains iron. Such 
substances may be made to assume a variety of amusing forms and 
positions by moving the magnet under the card, paper or table, on 
which they are placed. Toys, representing fishes, frogs, aquatic 
birds, &c., which are made to appear to bite at a hook, birds floating 
on the water, &c., are constructed on inaguetic principles, and sold 
in the shops. 

What is Elec- 1140. Electro-magnetism relates to magnet- 
tr<>-mag net ism? ] sm w pj c ] 1 i s induced by the agency of electricity. 

1141. The passage of the two kinds of electricity (namely, the 
positive and the negative) through their circuit is called the elec 
trie currents ; and the science of Electro-magnetism explains the 
phenomena attending those currents. It has already been stated 
that from the connecting wires of the galvanic circle, or battery, 
there is a constant current of electricity passing from the zinc to 
the copper, and from the copper to the zinc plates. In the single 
circle these currents will be negative from the zinc, and positive 
from the copper; but in the compound circles, or the battery, the 
current of positive electricity will flow from the zinc to the copper, 
and the current of negative electricity from the copper to the zinc. 
From the effect produced by electricity on the magnetic needle, it 
had been conjectured, by a number of eminent philosophers, that 
magnetism, or magnetic attraction, is in some manner caused by 
electricity. In the year 1819, Professor GErsted, of Copenhagen, 
made the grand discovery of the power of the electric current to 
induce magnetism ; thus proving the connexion between magnetism 
and electricity. In a short time after the discovery of Professor 
(Ersted, Mr. Faraday discovered that an electrical spark could be 
taken from a magnet; and thus the common source of magnetism 
and electricity was fully proved. In a paper published a few years 
ago, this distinguished philosopher has very ably maintained ihe 
identity of common electricity, voltaic electricity, magnetic electric¬ 
ity (or electro-magnetism), thermo-electricity, and animal electric¬ 
ity. The phenomena exhibited in all these five kinds of electricity 
differ merely in degree, and the state of intensity in the action of the 


ELECTKO-MAG NET ISM. 




3aia. Thb discovery of Professor CErsted has been followed out by 
AmpAre, who, by his mathematical and experimental researches, has 
presented a theory of the science less obnoxious to objections than 
that proposed by the professor. The discovery of CErsted was 
limited to the action of the electric current on needles previously 
magnetized ; it was afterwards ascertained by Sir Humphrey Davy 
and M. Arago that magnetism may be developed in steel not pre 
viously possessing it, if the steel be placed in the electric current. 
Both of these philosophers, independently of each other, ascertained 
that the uniting wire, becoming a magnet, attracts iron filings and 
collects sufficient to acquire the diameter of a common quill; but 
the moment the connexion is broken, all the filings drop off, and the 
attraction diminishes with the decaying energy of the pile. Filings 
of brass or copper, or wood-shavings, are not attracted at all. 


1142. All the effects of electricity and galvanism that have 
hitherto been described have been produced on bodies biter- 
posed between the extremities of conductors, proceeding from 
the positive and negative poles. It was not known, until the 
discoveries of Professor CErsted were made, that any effect 
could be produced when the electric circuit is uninterrupted.. 
What is the It will presently be seen that this constitutes the 
difference be- great distinction between electricity and electro- 
^ tricity and magnetism, namely, that one describes the effect 
electro-mag- of electricity when interrupted in its course, and 
netism l that ot j iei . more especially explains the effect of 
an uninterrupted current of electricity. 

What are the 1143. The principal facts in connexion with the 

^ facts^of elec sc ^ ence electro-magnetism are, — 
tro-magnet- (1.) That the electrical current, passing uninter . 
ism l ruptedly through a wire connecting the two ends 

of a galvanic battery, produces an effect upon the magnetic 
needle. 

(2.) That electricity will induce magnetism. 

(3.) That a magnet, or a magnetic magazine, will induce 
electricity.. 

(4.) That the combined action, of electricity and magnetism, 
as described in this science, produces a rotatory motion of cer¬ 
tain kinds of bodi< v s in a direction pointed out by certain laws. 

/5.) That the periodical variation of the magnetic needle 


310 


NATURAL PHILOSOPHY. 


from the true meridian, or, in other words, the variation of th$ 
compass, is caused by the influence of the electric currents. 

(6.) That the magnetic influence is not confined to iron, steel, 
&c., but that most metals, and many other substances, may be 
converted into temporary magnets by electrical action. 

(7.) That the magnetic attraction of iron, steel, &c., may be 
prodigiously increased by electrical agency. 

(8.) That the direction of the electric current may, in all 
cases, be ascertained. 

(9.) That magnetism is produced whenever concentrated elec¬ 
tricity is passed through space. 

(10.) That while in common electrical and magnetic attrac¬ 
tions and repulsions those of the same name are mutually 
repulsive, and those of different names attract each other, in 
the attractions and repulsions of electric currents it is precisely 
the reverse, the repulsion taking place only when the wires are 
so situated that the currents are in opposite direction. 

The consideration of the subject of electricity induced by 

magnetism properly belongs to the subject of Magneto-eleo 

tricity, in which connexion it will be particularly noticed. 

* 

How is the 1144. The direction of the electric current is 
turren^off° ascer t a iped by means of the magnetic needle. If 
electricity a sheet of paper be placed over a horse-shoe mag- 
ascertained l ne t, an( j fi ne b] ac k sand, or steel filings, be dropped 
loosely on the paper, the particles will be disposed to arrange 
themselves in a regular order, and in the direction of curve lines. 
This is, undoubtedly, the effect of some influence, whether that 
ot electricity, or of magnetism alone, is not material at present 
to decide. 


How will a 
freely-suspend¬ 
ed magnet place 
itself in relation 
to the electrical 
current ? 


1145 A magnet freely suspended tends 
to assume a position at right angles to the 
direction of a current of electricity passing 
near it. 


114(1. If a wire, which connects the extremities of a voltak 


KLECTE0-MAGHE7BM. 


an 


oatto y, be brought over and parallel with a magnetic needle a$ 
rest, or with its poles properly directed north and south, tha* 
end of the needle next to the negative pole of the battery will 
move towards the west, whether the wire be on one side of the 
needle or the other, provided only that it be parallel with it. 

1147. Again, if the connecting wire be lowered on either side 
of the needle, so as to be in the horizontal plane in which the 
needle should move, it will not move in that plane, but will have 
a tendency to revolve in a vertical direction; in which, however, 
it will be prevented from moving, in consequence of the attrac¬ 
tion of the earth, and the manner in which it is suspended 
When the wire is to the east of the needle, the pole nearest to 
the negative extremity4>f the battery will be elevated; and 
when it is on the west side, that pole will be depressed. 

1148. If the connecting wire be placed below the plane in 
which the needle moves, and parallel with it, the pole of the 
needle next to the negative end of the wire will move towaids 
the east, and the attractions and repulsions will be the reverse 
of those observed in the former case. 

How does the 1149. The action of the conducting-wire in 
electro-magnetic these cases exhibits a remarkable peculiarity, 
current act1 All other known forcet, exerted between two 
points act in the direction of a straight line connecting these 
points, and such is the case with electric and magnetic actions, 
separately considered; but the electric current exerts its mag* 
netic influence laterally, at right angles to its own course. Nor 
does the magnetic pole move either directly towards or directly 
from the conducting-wire, but tends to revolve around it without 
changing its distance. Hence the force must be considered as 
acting in the direction of a tangent to the circle in which the 
magnetic pole would move. 

What effect has 1150. The two sides of an unmagnetized 
kryTnunrnc.g- steel needle will become endued with the 
nutized s*e*l i north and south jx laxity, if the needle U* 


812 


natural philosophy. 


placed parallel with the connecting wire of a voltaic battery, 
and nearly or quite in contact with it. But, if the needle 
be placed at right angles with the connecting wire, it will 
become permanently magnetic ; one of its extremities point¬ 
ing Id the north pole and the other to the south, when it is 
'Yeely suspended and suffered to vibrate undisturbed. 

1151. Magnetism maybe communicated 
to iron and steel by means of electricity 
from an electrical machine; but the effect 
can be more conveniently produced by means 
of the voltaic battery. This phenomenon is 


Vo what may 
nagnetism be 
•communicated 
by the voltaic 
battery, and 
•chat is the pro- 
less called 1 

called electro-magnetic induction. 

What is a 1152. A Helix is a spiral line, or a line wound 
Hchx / into shape of a cork-screw. 

What use is 1153. If a helix be formed of wire, and a 
^connexion™ bar of steel be enclosed within the helix, on 
vith the battery ? applying the conducting-wires of the battery 
to the extremities of the helix, the steel bar will immediately 
become magnetic. The electricity from a common electrical 
machine, when passed through the helix, will produce the 
same effect. 


1154. The wire which forms the helix should 
be coated with some non-conducting substance, 
such as silk wound around it; as it may then 
be formed into close coils, without suffering tho 
electric fluids to pass from surface to surface, which would im¬ 
pair its effect. 

1155. If such a helix be so placed that it may move freely 
«s when made to float on a basin of water, it will be attracted 
and repelled by the opposite poles of a common magnet. 

1156. If a magnetic needle be surrounded by coiled wire, 
covered with silk, a very minute portion of electricity through 


And what must 
first be done 
l nth the wire of 
llie helix 1 


ELECTRO-MAGIS ETISM. 


u I 


the wire will cause the needle to deviate from its proper 
direction. 


What is av Elec- H*>7. A needle thus prepared is called an 
'ru-magnUic Electro-magnetic Multiplier. It is, in fact, a 
Multiplier? very delicate electroscope., or rather galvanom• 
eter, capable of pointing out the direction of the electric cur- 
rent in all cases. 


^ ^ ^ 1158. Among the most remarkable of the 

by the Electro- f acts connected with the science of electro 
magnetic Rota- magnetism is what is called the Electro¬ 
magnetic Rotation. Any wire through 
which a current of electricity is passing has a tendency to 
revolve around a magnetic pole in a plane perpendicular to 
the current, and that without reference to the axis of the 
magnet the pole of which is used. In like manner a mag 
netic pole has a tendency to revolve around such a wire. 


1159. Suppose the wire perpendicular, its upper end posi¬ 
tive, or attached to the positive pole of the voltaic battery, and 
its lower end negative; and let the centre of a watch-dial rep¬ 
resent the magnetic pole: if it be a north pole, the wire wnJ 
rotate round it in the direction that the hands move; if it be a 
south pole, the motion will be in the opposite direction. From 
these two, the motions which would take place if the wire were 
inverted, or the pole changed, or made to move, may be readily 
ascertained, since the relation now pointed out remains constant. 


1160. Fig. 166 represents the ingenious ap- 
F.Tvlain Fig. p ara t U s, invented by Mr. Faraday, to illustrate 
. the electro-magnetic rotation. The central pil¬ 

lar supports a piece of thick copper wire, which, on the one 
side, dips into the mercury contained in a small glass cup a. 
To a pin at the bottom of this cup a small cylindrical magnet 
is attached by a thread, so that one pole shall rise a little above 
the surface of the mercury, and be at liberty to move around 
She wire. The bottom of the cup is perforated, and hag a cop* 


NATURAL PHILOSOPHY. 


;u4 



per pin passing through it, which, touching the mercury on tne 
.nside, is also in contact with the wire that proceeds outwards, 

that side of the in¬ 
strument. On the other 
side of the instrument b , 
the thick copper wire, 
soon after turning down, 
terminates, but a thinnei 
piece of wire forms a 
communication between 
it and the mercury on 
the cup beneath. As 
freedom of motion is re¬ 
garded in the wire, it is made to communicate with the formei 
by a ball and socket-joint, the ball being held in the socket by 
a thread ; or else the ends are bent into hooks, and the one is 
then hooked to the other. As good metallic contact is required, 
the parts should be amalgamated, and a small drop of mercury 
placed between them ; the lower ends of the wire should also be 
amalgamated. Beneath the hanging wire a small circular mag¬ 
net is fixed in the socket of the cup b , so that one of its poles 
is a little above the mercury. As in the former cup, a metallic 
connexion is made through the bottom, from the mercury to the 
external wire. 

If now the poles of a battery be connected with the horizon¬ 
tal external wires c c, the current of electricity will be through 
the mercury and the horizontal wire, on the pillar which con 
nects them, and it will now be found that the movable part of 
the wire will rotate around the magnetic pole in the cup b , and 
the magnetic pole round the fixed wire in the other cup a, in the 
direction before mentioned. 

By using a very delicate apparatus, the magnetic pole ol the 
earth may be made to put the wire in motion. 

Explain Fig. H61. Big. 167 represents another ingenious 
1L7. contrivance, invented by M. Amp£r<* for Ulus- 




















ELECTROMAGNETISM. 


'U5 

trating the electro-magnetic rotation; and it has the advan. ge 
of comprising within itself the voltaic combination whicL ^ 
employed. It consists of a cylinder of copper 
about two inches high, and a little less than two 
inches internal diameter, within which is a small 
cylinder, about one inch in diameter. The two 
cylinders are connected together by a bottom, 
having an aperture in its centre the size of the 
smaller cylinder, leaving a circular cell, which 
may be filled with acid. A piece of strong cop¬ 
per wire is fastened across the top of the inner 
cylinder, and from the middle of it rises, at a 
right angle, a piece of copper wire, supporting a 
very small metal cup, containing a few globules of mercury. A 
cylinder of zinc, open at each end, and about an inch and a 
quarter in diameter, completes the voltaic combination. To the 
latter cylinder a wire, bent like an inverted U, is soldered at 
opposite sides ; and in the bend of this wire a metallic point ia 
fixed, which, when inserted in the little cup of mercury, sus¬ 
pends the zinc cylinder in the cell, and allows it a free circular 
motion. An additional point is directed downwards from the 
central part of the stronger wire, which point is adapted to a 
small hole at the top of a powerful bar magnet. When the 
apparatus with one point only is charged with diluted acid, and 
set on the magnet placed vertically, the zinc cylinder revolves 
ii a direction determined by the magnetic pole which is upper¬ 
most. With two points, the copper revolves in one direction 
and the zinc in a contrary direction. 

1162. If, instead of a bar magnet, a horse-shoe magnet be 
employed, with an apparatus on each pole similar to that which 
has now been described, the cylinders in each will revolve in 
opposite directions. The small cups of mercury mentioned in 
the preceding description are sometimes omitted, and the points 
ure inserted in an indentation on the inverted U.* 

* The plienomeuou of electro-uiagnetio rotatiou is beautifully illustrated 


Fig. 167. 






316 


NATURAL PHIL0S01HV. 


1163. The magnetizing power of the con- 
netizing 16 pov^r ducting wires of a battery is very greatly 
of the battery in- increased by coiling it into a helix, into 
which the body to be magnetized may be in¬ 
serted. A single circular turn is more efficient than a 
straight wire, and each turn adds to the power within a 
certain limit, whether the whole forms a single layer, or 
whether each successive turn encloses the previous one. 

How is a Mix n64 ' When a helix of 8 reat ^ ower ia 
of great power required, it composed of severa ’yers of 

wire. Th. ndre forming the coil must be 
insulated by being wound with cotton, to prevent any lat¬ 
eral passage of the current. 

1165. Fig. 168 represents a helix on a stand. 
Explain Fig. ^ b ar 0 f j ron being placed within 

the helix, is connected with the battery by 


Fig. 168. 



by Mi. Davis, in his treatise on Magnetism, to which reference has air each 
been made. He has invented and prepared a great variety of ingeninu; 
contrivances for the illustration of this subject, and his book should be ir 
the hands of all who desire a thorough acquaintance with all that has been 
discovered in the new department of science, in which magnetism and elec¬ 
tricity are combined. The author has *,eon indebted to Mr. Davis’ volurtf 
for a number of explanations which are incorporated in this work. 






ELECTROMAGNETISM. 


317 


mean?, tf the sciew-cups on the base of the stand. The twe 
extremities of the bar instantly become strongly magnetic, and 
keys, or pieces of iron, iron filings, nails, &c., will be held up 
so long as the connexion with the, battery is sustained. But, so 
soon as the connexion is broken, the bar loses its magnetic 
power, and the suspended articles will fall. The bar can be 
made alternately to take up and drop such magnetizable articles 
as are brought near it, as the connexion with the battery is 
made or broken. 


1166. A steel bar placed within the helix acquires the polar¬ 
ity less readily, but retains it after the connexion is broken. 
Small rods or bars of steel, needles, &c., may be made perma¬ 
nent magnets in this way. 

1167. A bar temporarily magnetized by 

What is an Elec- , . . . ,, , p,. 

iro-magnet ? the electric current is called an Electro- 

magnet. 


1168. To ascertain the poles of an elec- 
trf'a^dectro- 165 tro-magnet, it must be observed that tb* 
magnet be dis- north ])ole will be at the furthest end of 
the helix when the current circulates in 
the direction of the hands of a watch. 

1169 Magnets of prodigious power have been formed by 
means of voltaic electricity. 


What was the 
power of the 
electro-magnets 
constructed by 
Prof. Henry 
and Dr. Ten 
Eyck ? 


1170. An electro-magnet was constructed by 
Professor Henry and Dr. Ten Eyck which was 
capable of supporting a weight of 750 pounds. 
They have subsequently constructed another, 
which will sustain 2063 pounds. It consists of 
a bar of soft iron, bent into the form of a 


horse-shoe, and wound with twenty-six strands of copper bell- 
wire, covered with cotton threads, each thirty-one feet long, 
about eighteen inches of the ends are left projecting, so thav 
only twenty-eight feet of each actually surround the iron. Tim 
aggregate length of the coils is therefore 728 feet. Each strand 
27 * 


NATURAL RHILOSOPIIY. 


318 


is ground on a little less than an inch; in the middle of the 
horse-shoe it forms three thicknesses of wire; and on the ends, 
or near the poles, it is wound so as to form six thicknesses. Be 
ing connected with a battery consisting of plates, containing a 
little less than forty-eight square feet of surface, the magnet 
supported the prodigious weight stated above, namely, 2063 
pounds. 

1171. He- Fig. 169. 

Explain Fig. LIACAL R ING . 

IKU 

Fig. 169 rep¬ 
resents a heliacal ring, or ring 
of wire bent in the form of a 
helix, with the ends of the 
wire left free to be inserted 
in the screw-cups of a bat¬ 
tery. Two semicircular pieces 
of soft unmagnetized iron, 

(urnished with rings, — the 
upper one for the hand, the 
lower one for weights,— 
are prepared to be inserted 
into the helix, in the manner 
of the links of a chain. As 
soon as the ends of the helix 
are inserted into the screw- 
cups of the battery, the rings will be held together, with great 
force, by magnetic attraction. 

1172. That the attraction is caused, or that the magnetism is in¬ 
duced, by the circulation of electricity around the coils, may be 
proved by the following interesting experiment. Hold the heliacal 
ring horizontally over a plate of small nails, and suspend an unmag- 
nctized bar perpendicularly on the outside of the ring, over the nails, 
and there will be no attraction. Suspend the bar perpendicularly 
through the helix, and the nails will all attach themselves to it in 
the form of tangents to the circles formed by the coils of the helia¬ 
cal ring. 



lieu) are horse- 
tfioe magne* 


1173. Communication of Magnetism to Steel 
by the Electro- magnet .— Bars of the U form 












ELECTROMAGUETIC TELEGRAPH. 




most readily are most readily magnetized by drawing them 
from the bend to the extremities, across the 
poles of the U electro-magnet, in such a way that both halves 
of the bar may pass at the same time over the poles to which 
they are applied. This should be repeated several times, recol¬ 
lecting always to draw the bar in the same direction. 

1174. Fig. 170 represents the U electro¬ 
magnet ; with the bar to be magnetized. When 
the bar is thick, both surfaces should be drawn 
across the electro-magnet, keeping each half applied to the 
same poie. To remove the magnetism, it is only necessary to 


Explain Fig. 
170. 


Fig. 170. 



reverse the process by which it was magnetized, that is, to draw 
the bar across the electro-magnet in a contrary Erection. 

1175. The Electro-magnetic Telegraph* 

On what fundo- — From the description which has now been 
mental principle r 

is the Electric given of the electro-magnetic power, it will 

Telegraph con- readily be perceived that a great force can be 
constructed / , , . , , , . . 

made to act simply by bringing a wire into 

contact with another conductor, and that the force can be in¬ 
stantly arrested in its operation by removing the wire from the 
contact; in other words, that by connecting and disconnecting 
a helix with a battery, a prodigious power can be made succes 

* The word telegraph is compounded of two Greek words, Tt]Xt {tele), sig 
nifjing at a distance, and yfjuif o {grapho), to write, that is, to signify or to 
write at a distance. The word telescope is another compound of the word 
nils with the word axon.su: (scepio), to see,— an instrument to see at a die 
an ce. 





























NATURAL PHILOSOIHY 




sively to act and cease to act. Advantage has been taken o 
this principle in the construction of the American electro-mag 
netic telegraph, which was matured by Professor Morse, and 
first put into operation between the cities of Baltimore and 
Washington, in 1844.* It was not, however, 
ZJ'rmdlreTThe untiI Profe3sor Henry, of Princeton, New Jor- 
magnetic tele- sey, had discovered the mode of constructing 
oraph possible ? ^ p 0wer f u i electro-magnets which have been 
noticed, that this form of the telegraph became possible. 

1176. The principles of its construction may 

Explain the man- ^ k r i e fly stated as follows : 
ner m which the J 

electric telegraph An electro-magnet is so arranged with its 
performs its armature that when the armature is attracted 
it communicates its motion to a lever, to which 
a blunt point is attached, which marks a narrow strip of paper, 
drawn under it by machinery resembling clock-work, whenever 
the electro-magnet is in action. When the electro-magnet ceases 
to act, the armature falls, and, communicating its motion to the 
lever, the blunt point is removed from its contact with the paper. 
By this means, if one of the wires from the battery is attached 
to the screw-cup, whenever the other wire is attached to the 
remaining cup the armature is powerfully attracted by the 
magnet, and the point on the lever presses the paper into the 
groove of a roller, thereby making an indentation on the paper, 
corresponding in length to the time during which the contact 
with the battery is maintained, the paper being drawn slowly 
under the roller. 

1177. In the construction of the electric tele¬ 
graph the first object of consideration is the devel¬ 
opment of the agent. The agent is the electric 
fluid, which is brought into action by a powerful 
battery. 

* For a particular description of this wondorful invention, the student is 
referred to Davis’ treatise on Magnetism, in which the parts are all de¬ 
scribed with a minuteness which leaves little more to be desired. Tht 
history, also, of the successive steps by which it was brought to its present 
degree of perfection, is to be found in the same connexion. 


What is the 
agent in the 
electric tele¬ 
graph l 


EL KCTRO-M AGNETHJ TELEGRAPH. 


3 21 


Fig. 171 represents a battery composed ol 
&xp am ig. twe j ve CU p Sj on the principle of Grove’s battery, 
each cup containing a thick cylinder of zinc, 
with a porous cell, two acids, and a strip of platinum, as 
described in Fig. 1G4. The chemical action of the acids on the 


Fig. 171 



zinc generates a powerful current of electricity towards the 
screw-cups at A B. 

1178. The second step in the construction of 
Explain Fig. telegraph is represented by Fig. 172. The 

wires from the battery represented in Fig. 171 
are carried to the screw-cups in the apparatus represented by 
Fig. 172, called the sig¬ 
nal-key, A to A and B 
to B, respectively. It 
will be observed that the 
cups of the signal-key are 
insulated, and that the 
electric fluid can finish its 
circuit only when the fin¬ 
ger depresses the knob 
and makes it come in con¬ 
tact with the metallic strip below, thus forming a communication 
between the screw-cups. The signal-key thus regulates the com¬ 
pletion of the circuit, and the flow of the current of electricity, 
at the will of the operator. 
















































































































322 


NATUKAL PHILOSOPHY. 


Expla 

ITS. 




Fig. 173 


1179. The signal-key is made m severa 
forms in the different telegraphs, and in Fig. 
173 is represented in its more perfect construe* 
tion. It consists of a lever, mounted on a horizontal axis, with 
a knob of ivory for the hand at the extremity of the long arm, 
which is at the left in 
the cut. This lever is 
thrown up by a spring, 
bo as to avoid contact 
with the button on the 
frame below, except when 
the lever is depressed for 
the purpose of com¬ 
pleting the circuit. A regulating screw is seen at the extremity 
of the short arm of the lever, which graduates precisely the 
amount of motion of which it is at any time susceptible. 

llSffi The third and last part of the tele¬ 
graph is the registering apparatus, represented 
in Fig. 174. 

Here are two screw-cups, for the insertion of the wires from 
a, distant battery. An iron in the shape of a U magnet stands 



Explain 

174 . 


Fit 


Fig 174 



at the left of the screw-cups, each arm of which is surrounded 
by a helix or coil of wire, the ends of which, passing down through 
the stand, are connected below with the screw-cups. It will 
then be seen that when the signal-key is depressed the electric 
circuit is completed, and that the electricity, passing through 
die coils of wire, renders the U-shaped iron highly magnetic 








ILIJSUTKO-MAGNETIC TELLvlcAPH. / 


Pig. 176. 






















824 


NATURAL PHILOSOPHY. 


and it attracts the armature down. The armature, is fixed to 
the shorter arm of a lever, and when the shorter arm is attracted 
down, the longer arm, with a point affixed, is forced upward and 
makes an indentation upon a strip of paper. The length of the 
indentation on the paper will depend on the length of time that 
the signal-key is depressed. When the signal-key is permitted 
again to rise, the electric current is broken, the U-shaped iron 
ceases to be a magnet, and, the armature being no longer 
attracted, the weight of the longer arm will cause that arm to 
fall, and no mark is made on the paper. 

When the telegraph was first constructed, it was thought nec 
essary to have two wires in order to form the circuit. It has 
since been found that the earth itself will serve for one-half the 
circuit, and that one wire will alone be necessary to perform the 
work of the telegraph. 

1180. Fig. 175 represents the manner in which 
Explain Fig. the electric telegraph is put into operation. On 
the left of the figure is seen the operator, with 
the battery at his feet and his finger on the signal-key. From 
one screw-cup of the battery extends a wire which traverses 
the whole distance between two cities, elevated on posts for 
security. In the distant city the wire reaches another screw- 
cup to which it is attached, while from another screw-cup at tho 
same station another wire is attached, which extends back to the 
operator first mentioned. The depression of the signal-key 
forms a connexion between the two poles of the battery by 
means of the wire, and the fluid will traverse the whole distance 
between the two stations in preference to leaping over the space 
between the two screw-cups. The right of the figure represents 
the receiver of the information, reading the message which has 
thus been imprinted by the point. 


1182. In the preceding figures the mere out* 
Explain Fig. jj nes have been gi ven> j n or d er that they may 
be distinctly understood. To present the strip 
uf paner so that it may readily receive the impression, auli- 


F.LKCTKO M AG NET .0 TEi*EG HA PH. 


32 5 

tiona) machinery becomes necessary. The complete registering 
machine is shown in hhg. 176, in which S represents a huge 


Fig. 176. 



spool on which the paper is wound, and clock-work witn rollers 
fco give the paper a steady motion toward the point by which tb« 
marks are to be made. A bell is sometimes added, which \z 
struck by a hammer when the lever first begins to more, in 
order to draw the attention of the operator. 

1183. It will be recollected that this form of the magnetic 
telegraph is familiarly known as Morse’s, the machine making 
nothing but straight marks on the slip of paper. But these 
straight marks maj be made long or short, at the pleasure of .he 
operator. If the key be pressed down and "'ustantly be per 
mitted to rise, it will make a short line, not longer than a 
hyphen. By means of a conventional alphabet, in which the let¬ 
ters are expressed by the repetition and combination of marks 
varying in length, any message may be conveniently spelt out, 
so as to be distinctly understood at the distant station. These 
are the essential features of Morse’s Telegraph. 

28 






NATURAL PHILOSOPHY. 


\ 


m 

1184. It is necessary, in long lines of telegraphs, to combine tii« 
effects of several batteries to supply the loss of power in traversing 
iong circuits. This is done by local batteries or relays, as they are 
sometimes called, familiarly known in connexion with Morse's tele¬ 
graph. The use of the relays may be dispensed with by increasing 
the power of the battery, or distributing it in groups along the line 
It is sometimes divided by arranging one-half at each end of the 
line For every twenty miles an addition of one of Grove’s pint 
eups should be made. The expense of acids for each cup for two 
days does not much exceed one cent. For a line of telegraph 
extending around the earth, twelve hundred Grove’s cups would be 
required, distributed at equal distances, fifty in a group. 

1185. Bain’s Telegraph. — The telegraph known by the 
name of Bain’s telegraph, the simplest now in use, differs from 
Morse’s principally in its mode of registering. It performs its 
work by the decomposition of a saline solution. The pen or 
point is stationary. A circular tablet, moved by clock-work, 
under the point, receives the point in concentric grooves, and 
the writing is arranged in spiral lines, occupying but little 
space. 

Explain Fig. 177 represents Bain’s telegraph. The pen 
Eig. 177. holder is connected with the positive wire of the 
battery, and the tablet with the negative. The circuit is com* 


Fig. 177. 



f 















ELECTRO-MAGNETIO TELEGRAPH. 


827 


pleted by-paper moistened with a solution of the yellow prus- 
siate df potash, acidulated with nitric or sulphuric acid. The 
pen-wire is of iron. When the circuit is completed, the solution 
attacks the pen, dissolves a portion of its iron, and forms the 
color known as Prussian blue, which stains the paper. The 
alphabet used by this line is the same in principle as that used 
m the telegraph of Morse. The advantage of this telegraph 
consists in the rapidity with which the disks at both ends are 
made to revolve, by which a message may be communicated at 
the rate of a thousand letters in a minute. 


Explain 1186. The 
Fig. 178. ca ll commonly 
used in connexion with 
Bain’s telegraph is rep¬ 
resented in Fig. 178. It 
consists of a U magnet, 
each arm surrounded by 
a helix of wires, which, 
when the current passes, 
causes the armature to 
be attracted and give mo¬ 
tion to machinery, by 
which a bell or a glass is 
rung. 



Fig. 178. 


Explain 1187. Fig. 
tig. 179. p 79 represents 
form. The armature is 
mounted on an upright 
bar, directly before the 
poles of the U magnet, 
which is surrounded by 
many coils of insulated 
wire. In this magnet 
the points of contact are 
preserved from oxidation 
by the use of platinum. 


the receiving magnet in its improved 
Fig. 179. 







NATURAL PHILOSOPHY. 


328 

1188. House’s Printing Telegraph. — This telegraph differs 
Prom the other principally in its printing with great rapidity 
the letters which form the message. 

Explain 1189. Fig. 180 represents the mechanical part of 
Fig. 180. House's telegraph. The operator sits at a key-board 
similar to that of a pianoforte or organ, and, by depressing a 


key, the letter corresponding with the key is made to appear at 
a little window at the top of the instrument, while it is at the 
same time printed on a strip of paper below. The principle by 
which this exceedingly ingenious operation is performed is 
simply this: A given number of electrical impulses are given 
for each letter. These impulses give motion to a wheel, so that 
on the depression of a key the circuit will be broken at precisely 
the point which corresponds with the letter. The machinery 
by which this is effected is necessarily complicated and it falls 
not within the province of this work to go fu ther into the 
explanation. The whole process is described in Davis’ Book of 
the Telegraph, to which this volume is indebted for most of A he 
particulars which have been given in relation to the subject. 



Fig. 130. 












ELECTRO MAGNETIC TELEGRAPH. 




The following history of the electric telegraph in this country is extracted 
from the Portland Advertiser, and deserves a place in this connexion : 

The electric telegiaph, being used solely for the conveyance of news 
and communications, is so intimately connected with posts and post-ofiices, 
that a brief sketch of its rapid progress in the United States is here given. 

“ It is to American ingenuity that we owe the practical application of 
the magnetic telegraph for the purpose of communication between distant 
points, and it has been perfected and improved mainly by American science 
and skill. While the honor is due to Professor Morse for the practical 
application and successful prosecution of the telegraph, it is mainly owing 
to the researches and discoveries of Professor Henry, and other scientiho 
Amexicans, that he was enabled to perfect so valuable an invention 

“ The first attempt which was made to render electricity available for 
the transmission of signals, of which wo have any account, was that of 
Lesage, a Frenchman, in 1774. From that time to the present there have 
been numerous inventions and experiments to effect this object ; and, from 
1820 to I860, there were no less than sixty-three claimants for different 
varieties of telegraphs. We will direct attention only to those of Morse. 
Lain and House, they being the only kinds used in this country. 

“ During the summer of 1832, Professor S. F. B. Morse, an American, con¬ 
ceived the idea of an electric or electro-magnetic telegraph, and, alter 
numerous experiments, announced his invention to the public in April, 1837. 

“ On the 10th of March, 1837, Hon.- Levi Woodbury, then Secretary of 
the Treasury, issued a circular requesting information in regard to the 
propriety of establishing a system of telegraphs for the United States, to 
which Professor Morse replied, giving an account of his invention, its pro¬ 
posed advantages and probable expense. At that time ‘ he presumed five 
words could be transmitted in a minute.’ 

“ In 1838, the American Institute reported that Morse could telegraph 
the words * steamboat Caroline burnt ’ in six minutes. Now, a thousand 
such words are telegraphed in two minutes. 

“ In 1844, Congress built an experimental line from Baltimore to Wash¬ 
ington, to test its practical operation. That line was soon continued on to 
Philadelphia and New York, and reached Boston the following year. Two 
branches diverge from this line, one from Philadelphia to St. Louis, 1000 
miles, the other from New York, via Buffalo, to Milwaukie, 1300 miles 
long. One also, 1400 miles in length, goes from Buffalo to Lockport, and 
from thence through Canada to Halifax, N. S., whence there is a continuous 
line through Portland to Boston. The great Southern line, from Washing¬ 
ton to New Orleans, is 1700 miles long. Another, 1200 miles, running to 
New Orleans from Cleveland, Ohio, via Cincinnati. The best paying line, 
it is said, is that between Washington and New York, which, during six 
months of last year, transmitted 154,514 messages, valued at $08,490 ; and 
the receipts for the year ending July, 1852, were $103,000. The average 
performance of the Morse instruments is from 8000 to 9000 letters per 
hour. The cost of construction, including wire, posts, labor, &c., is about 
$150 per mile. The Bain telegraph extends in the United States 2012 
miles, and House’s 2400 miles, making a total, with Morse’s, of 89 lines, 
embracing 16,729 miles. At how many way stations the magnetic current 
is arrested and messages conveyed, wo are not informed. Thus, in less 
than nine years, from a feeble beginning, under the fostering aid of govern¬ 
ment, have its wires and news communications spread all over the country. 

“ The astonishing results of the telegraph, victorious even in a run 
against time, are remarkable in the United States. The western cities, 
having a difference of longitude in their favor, actually receive news from 
New York sooner by the clock than it is sent. When the Atlantic made 
her first return voyage from Liverpool, a brief account of the nev/s wai 

28 * 


NATURAL PHILOSOPHY. 


a;30 


•■elegiaphed to New Orleans at a few minutes 'after noon (New York tin?"), 
and reached its destination at a few minutes before noon (New (.xleans 
time), and was published in the evening papers of both cities at tho same 
dour. This is now a daily occurrence. 

“Through its instrumentality (we mean no pun) Webster’s death was 
simultaneously made known throughout the length and breadth ot our 
land, and the next morning the pulpits from Maine to New Orleans were 
echoing in eu'ogies to his greatness, and mourning his departure. 

“ The great extent of the telegraph business, and its importance to the 
community, is shown by a statement of the 'amount paid for despatches by 
the associated press of New York, composed of the seven principal morning 
papers, — the Courier and Enquirer, Tribune, Herald, Journal of Commerce, 
Sun, Times and Express. During the year ending November 1, 1852, 
these papers paid nearly $50,U0O for despatches, and about $14,000 
jor special and exclusive messages, not included in the expenses of the 
association. 

“ The difference between Morse’s and House’s telegraph is, principally, 
that the first traces at the distant end what is marked at the other ; while 
House’s does not trace at either end, but makes a signal of a letter at the 
distant end which has been made at the other, and thus, by new machinery, 
and a new power of air and axial magnetism, is enabled to print the signal 
letter at the last end, and this at the astonishing rate of sixty or seventy 
strokes or brakes in a second, and at once records the information, by its 
own machinery, in printed letters. Morse’s is less complicated, and more 
easily understood; while House’s is very difficult to be comprehended in its 
operations in detail, and works with the addition of two more powers, — 
one air, and the other called axial magnetism. One is a tracing or writing 
telegraph, the other a signal and printing telegraph. 

“ The telegraphs in England are next in importance and extent to those 
in this country. They were first established in 1845, and there are about 
4000 miles of wire now in operation. 

“ The charge for transmission of despatches is much higher than in 
America, one penny per word being charged for the first fifty miles, and 
one farthing per mile for any distance beyond one hundred miles. A 
message of twenty words can be sent a distance of 500 miles in the United 
States for one dollar, while in England the same would cost seven dollars ” 

1190. The Electrical Fire Alarm. —The principle of the electric 
telegraph has recently been applied to a very ingenious piece of 
mechanism, by which an alarm of fire may be almost instantly com¬ 
municated to every part of a large city. Wires, extending from 
the towers of the principal public buildings in which large bells 
are suspended, unite at a central point, where the operator is in 
constant attendance. On an alarm of fire in any locality, the watch 
or police of the district goes to a small box, kept in a *onspieuous 
place, which he opens, and makes a telegraphic communication to the 
central operator, who, immediately recognizing the signal and the 
district from which it came, gives the alarm, by making each bell 
in connexion with the telegraph strike the number corresponding 
with the district in which the alarm commenced. By this means 
the alarm is communicated simultaneously to all parts of the city. 
This ingenious application of scientific principles has been in sue* 
cessful operation In the city of Boston long enough to prove its 
gieat value. 


KLEGTROTY FiL PROCESS. JJ.\1 

1191. Thy Atmospheric Telegraph. — An ingenious appar 
at us, called “ The Atmospheric Telegraph ,” has recently been 
constructed by Mr. T. S. Richardson, of Boston, designed to 
send packages through continuous tubes by means of atmos¬ 
pheric pressure.. An air-tight tube being laid between two 
places, either under or above ground, a piston, called by Mr. 11. 
a plunger , is accurately fitted to its bore, behind which the 
package designed to be sent is attached. The air having been 
exhausted from the tube by engines at the opposite end, the 
pressure of the atmosphere will drive the piston, or plunger 
with its load, forward to its proposed destination. 

This ingenious application of atmospheric pressure operates 
with entire success in the model, and has been also successfully 
tested in tubes that have been laid to the extent of a mile. Pa¬ 
tents have been secured for the invention in England, France, 
and other countries of Europe, as well as in this country; and 
a company is now forming for testing the principle between the 
cities of Boston and New York. The air is to be exhausted 
from the tubes by means of steam-engines, and there are to be 
intermediate stations between those two cities. 

1192. The Electrotype Process. — This process, known by 
the various names electrotype, electro plating and gilding, ga.l- 
vanotype, galvano-plastic, electro-plastic and electro-metallurgy, 
is a process by which a coating of one metal is made to adhere 
to and take the form of another metal, by electrical agency. 

1193. It is a process purely chemical and electrical, and the con 
sideration of the subject pertains more properly to the science of 
Chemistry. As this volume has not professed to pursue a rigid 
classification, it may not be amiss to give this brief notice of the 
process. 

1194. It consists in subjecting a chemical solution of one 
metal to electrical action with another metal. A solution of a 
salt or oxide, having a metallic base, forms part of the electric 
circuit, and, by the electrical action, the oxygen or acid will be 
drawn to the positive end of the circuit, while the pure metal 
will be forced to the negative pole, where it will either combine 


NATURAL PHILOSOPHY. 


with the metal or adhere to it, taking Its exact form. Pho 
thickness of the coating of the pure metal will depend on the 
length of time that the body to be coated is subjected to tho 
combined action, chemical and electrical. Hence a mere film 
or a solid crust may be attached to any conducting substance. 

When a substance not in itself a conductor is to be coated, it 
must first be made a conductor by covering its surface with 
some substance which will impart the conducting power. This 
is usually effected by means of finely-powdered black lead. 

1195. When a part only of a body is to be coated by the 
electrotype process, the parts which are to remain uncoated must 
previously be protected by means of a thin covering of wax, 
tallow or some other non-conducting substance. 

1196. Magneto-electricity. — Mag- 
ZtfekctJaly? neto-electricity treat? of the developrren. 
of electricity by magnetism. 

How is Ma°- 1197. Electric currents are excited in a 
veto-electricity conductor of electricity by magnetic changes 
developed i taking place in its vicinity. Thus, the 
movement of a magnet near a metallic wire, or near an iron 
bar enclosed in a wire coil, occasions currents in the wire. 

1198. When an armature, or any piece of soft iron, is 
brought into contact with one or both of the poles of a magnet, 
it becomes itself magnetic by induction, and by its reaction 
adds to the power of the magnet: on the contrary, when 
removed from the contact, it diminishes the power of the mag* 
net, and these alternate changes in its magnetic state induce a 
current of electricity. *. 

1199. The most powerful effects are obtained 

How are the ^ causing a bar of soft iron, enclosed in a 

most power Jut J ® ’ 

effects of mag- helix, to revolve by mechanical means near the 

neto-electricity poles of a steel magnet. As the iron approaches 
the poles in its revolution, it becomes mag¬ 
netic ; as is recedes from them, its magnetism disappears; and 


MAGNETO-ELECTRICITY. 


333 


this alternation of magnetic states causes the flow of a current 
of electricity, which may be directed in its course to screw- 
cups, from which it may be received by means of wires con¬ 
nected with the cups. 


Explain Fi 
181 . 


1200. The Magneto-electric Machine.— 
Fig. 181 represents the magneto-electric ma¬ 
chine, in which an armature, bent twice at 
right angles, is made to revolve rapidly in front of the poles of 
a compound steel magnet of the U form. The U magnet, whose 



north pole is seen at N, is fixed in a horizontal position, with its 
poles as near the ends of the armature as will allow the latter 
to rotate without coming into contact with them. The armature 
is mounted on an axis, extending from the pillar P to a small 
pillar between the poles of the magnet. Each of its legs is 
enclosed in a helix of fine insulated wire. The upper part of 
the pillar P slides over the lower part, and can be fastened in 
any position by a binding screw. In this way the band con¬ 
necting the two wheels may be tightened at pleasure, by in¬ 
creasing the distance between them. This arrangement also 
renders the machine more portable. By means of the multiply - 
ing-wheel W, which is connected by a band with a small wheel 
on the axis, the armature is made to revolve rapidly, so that 
the magnetism induced in it by the steel magnet is alternately 












334 


NATURAL PHILOSOPHY. 


destroyed and renewed in a reverse direction to the previous 
one. When the legs of the armature are approaching the mag¬ 
net, the one opposite the north pole acquires south polarity, and 
the other north polarity. The magnetic power is greatest while 
the armature is passing in front of the poles. It gradually 
diminishes as the armature leaves this position, and nearly dis¬ 
appears when it stands at right angles with the magnet. A* 
each leg of the armature approaches the other pole of the U 
magnet, by the continuance of the motion magnetism is again 
induced in it, but in the reverse direction to the previous one. 
These changes in the magnetic state of the armature excite 
electric currents in the surrounding helices, powerful in propor 
tion to the rapidity with which the magnetic changes are pro¬ 
duced. 

1201. Shocks may thus be obtained from the machine, and, if the 
motion is very rapid, in a powerful machine the torrent of shocks 
becomes insupportable — the muscles of the hands which grasp the 
handles are involuntarily contracted, so that it is impossible to 
loosen the hold. The shocks, however, are instantly suspended by 
bringing the metallic handles into contact. 

1202. Thermo-electricity. — Thermo- 
What is Ther- , , . . „ „ . ^ . . 

mo-electricity ? electricity expresses a iorm ot electricity 

developed by the agency of heat. 

1203. In the year 1822, Professor Seebeck, of L jrlin, dis¬ 
covered that currents of electricity might be produced by the 
partial application of heat to a circuit composed exclusively of 
solid conductors. The electrical current thus excited has been 
termed Thermo-electric (from the Greek Thermos, which signi¬ 
fies heat), to distinguish it from the common galvanic current; 
which, as it requires the intervention of a Jhiid element, was 
denominated a Hydro-electric current. The term Stereo-electric 
current has also been applied to the former, in order to mark 
its being produced in systems formed of solid bodies alone. It 
is evident that if, as is supposed in the theory of Ampere, mag 
nets owe their peculiar properties to the continual circulation 
of electric currents in their minute parts, these currents v r ib 
come under the description of the stereo-electric currents. 


TH EKMO-ELECTRICITY.-ASTKON OMY. 835 

1204. From the views of electricity which have now been 
given, it appears that there are, strictly speaking, three states 
of electricity. That derived from the common electrical ma¬ 
chine i& in the highest degree of tension, and accumulates until 
it is able to force its way through the air, which is a perfect 
non-conductor. In the galvanic apparatus the currents have a 
smaller degree of tension; because, although they pass freely 
through the metallic elements, they meet with some impedimenta 
in traversing the fluid conductor. But in the thermo-electric 
currents the tension is reduced to nothing ; because, throughout 
the whole course of the circuit, no impediment exists to its free 
and uniform circulation. 

1205. If the junction of two dissimilar metals be heated, an 
eieetrical current will flow from the one to the other. 

1206. Instead of two different metals, one metal in differen* 
conditions can be used to excite the current. 

1207. Metals differ greatly in their power to excite a cur¬ 
rent when associated in thermo-electric pairs. A current may 
be excited with two wires of the same metal, by heating the 
end of one, and bringing it into contact with the other. This 
experiment is most successful when metals are used that have 
the lowest conducting power of heat. 

1208. Thermo-electric batteries have been constructed with 
suf&cicnt power to give shocks and sparks, and produce various 
magnetic phenomena, indicative of great magnetic power; but 
the limits of this volume will not allow a further consideration 
of the subject. 

1209. Astronomy. — Astronomy treats 
HJiat isAstron- ^ ^ heavenly bodies, the sun, moon, plan¬ 
ets, stars and comets, and of the earth as a 
member of the solar system. 

1210. The study of astronomy necessarily involves an acquaint¬ 
ance with mathematics, but there are many interesting facts, which 
have been fully established by distinguished astronomers, which 
ought to be familiar to those who have neither the opportunity i»<>r 


38(? NATURAL PHILOSOPHY. 

the leisure to pursue the subject by the aid of mathematical light 
To such the following brief notice of the subject will not be devoid 
of interest 

1211. Some of the mqst distinguished men who 
W7to are some have contributed to the great mass of facts and 
of the most, dis- laws which make up the science of Astronoiny 
tinguished As- were Hipparchus, Ptolemy, Pythagoras, Copern i- 
tronomers ? cus, Tycho Brahe, Galileo, Kepler and Newton. 

The present century has added to this list many 
others whose fame will descend to posterity with great lustre. 

1212. Hipparchus is, usually considered the father of Astronomy, 
lie was born at 'Nicaea, and died about a hundred and twenty-five 
years before the Christian era. He divided the heavens into con¬ 
stellations, twelve in the ecliptic, tw r enty-one in the northern, and 
sixteen in the southern hemisphere, and gave names to all the stars. 

He discovered the difference of the intervals between the autum¬ 
nal and vernal equinoxes, and, likewise, by viewing a tree on a 
plain, and noticing its apparent position from different places of 
observation, he was led to the discovery of the parallax of the heav¬ 
enly bodies ; that is, the difference between their real and apparent 
position, viewed from the centre and from the surface of the earth, 
lie determined longitude and latitude, fixing the first degree of lon¬ 
gitude at the Canaries. 

1213. Ptolemy flourished in the second century of the Christian 
era. lie was a native of Alexandria, or Pelusium. In his system 
he placed the earth in the centre of the universe,— a doctrine univer¬ 
sally adopted and believed until the sixteenth century, when it was 
confuted and rejected by Copernicus. Ptoiemy gave an account of 
the fixed stars, and computed the latitude and longitude of one thou¬ 
sand and twenty-two of them. 

1214. Pythagoras was born at Samos, and his death is supposed 
to have taken' place about five hundred years before the Christian 
era. He supposed the sun to be the centre of the universe, and 
that the planets revolved around him in elliptical orbits. This doc¬ 
trine, how r ever, was deemed absurd until it was established by Co 
pernicus in the sixteenth century. 

1215. Tycho Brahe, a Danish astronomer, flourished about the 
middle of the sixteenth century. His astronomical system was sin¬ 
gular and absurd, but the science is indebted to him for a more cor 
rect catalogue of the fixed stars, and for discoveries respecting the 
motions of thg moon and the comets, the refraction of the rays of 
light, and for many othei important improvements. To him, also, 
was Kepler indebted for the principal facts which were the basis of 
nis astronomical labors. 

1216. Copernicus v as born in Prussia, in the latter part of the 
fifteenth century. lib revived the system of Pythagoras, which 
placed the sup in the centre of the system, lie taught the true 
doctrine that the apparent motion of the heavenly bodies is caused 
by the real motion of the earth. But, for nearly a century afYn 
the publication of his system, he gained but few followers. 


AJ5TKONOMY. 


Galileo, a native of Pisa, flourished in the latter part of 
ine sixteenth century. By^ his observation of the planets Venus and 
j upiter, he gained a decisive victory for the Copernican system. He 
persecuted and imprisoned by the inquisition for holding what 
thought, in that age of ignorance and superstition, to be heret¬ 
ical opinions, and compelled on his knees to abjure the truths 
whi *h he had discovered, and which he had too much sense to dis¬ 
believe. Notice has already been taken of this distinguished phi¬ 
losopher in connexion with the laws of falling bodies (see page 52), 
for the discovery of which the world is indebted to him. 

1213. Kepler, who, from his great discoveries, is called the legis- 
ator of the heavens, was a native of Wirtemberg, in 1571. Availing 
himself of the observations of Tycho Brahe, he discovered three 
great laws, known as Kepler’s laws of the planetary motions, and on 
them were founded the discoveries of Newton, as well as the whole 
modern theory of the planets. 

Kepler’s laws could not have been discovered but for the observa¬ 
tions of Tycho Brahe (as Kepler was not himself an observer), and 
no further discoveries could have been made than Kepler made but 
for the telescope of Galileo. It has elsewhere been stated that 
Galileo was indebted to Jansen, of Holland, for the idea of the 
telescope. But, since the days of Galileo,/the telescope has been 
most wonderfully improved, and invested with almost inconceivable 
powers. Herschel computed that the power of his telescope was so 
great as to penetrate a space through which light (moving with the 
prodigious velocity of 200,000 miles in a second of time) would 
require 350,000 years to reach us. But the great telescope of Lord 
Rosse would probably reach an object ten times more remote. 

1219. Sir Isaac Newton, who has been called the Creator of 
Natural Philosophy, was born in Lincolnshire, England, in 1642. 
His discovery of the universal law of gravitation, and many other 
valuable and important contributions which he made to science, 
place him among the foremost of those to whom the world is in¬ 
debted for an insight into the magnificent displays of the material 
world. 

1220. According to the system cf As- 

Grive an ac- ° * 

count of the tronomy which is now universally 

solar system as gun j g the centre of a system of heavenly 
now adopted. . 

bodies, called planets, which revolve around 

him as a centre. 

Secondly. The earth is one of these planets. 

Thirdly. That some of these planets are attended bv 
satellites or moons, which revolve around their respective 

planets, and with them around the sun. 

29 



NATUi :A T , RilILOSOFlIJr' 




Fourthly. That the size, distance and rapidity of 
motion of each of these planets is known to be different. 

Fifthly. That the stars are all of them suns, with 
systems of their own, and probably many, if not all of 
them, having planets, with their moons revolving around 
them as centres. 

Sixthly. That there is a central point of the universe, 
around which all systems revolve. 

whatismeant 1221 - ° F ™ E SoLA * System.— By the 
by the Solar Solar System is meant the sun and all the 
System? heavenly bodies which revolve around it. 
These are the planets with their satellites or moons, our 
earth with its moon, together with an unknown number 
of comets. 


What are 1222. Of the Pkimary Planets. — Those 
Primary bodies which revolve around the sun, with¬ 
out revolving, at the same time, around 
some other central body, are called Primary Planets. 

9iwfh*name» . 1223 ’ For ma y y ears the P ,anets were C0D - 
of the eight sidered to be six in number only, and they were 

'primary all, except our ear'll, named after the gods o* 
p anets. heathen mythology,—Mercury, Venus, Earth, 

Mars, Jupiter, and Saturn. In the year 1781, Sir William 
ilerschel discovered another, to which the name of Uranus has 
been given; and in the year 1846 an eighth was discovered, to 
which the nan e of Le Verrier was at first given, from a dis¬ 
tinguished Frei ch astronomer, by moans of whom it was pointed 
out. It is now known by the name of Neptune. 

Hem many 1224. Besides these primary planets, it wa? 
mary planets dlscovered > between the years 1800 and 1807, 
have been dis - that between Mars and Jupiter there were four 
covered? smaller planets, of such diminutive size, compared 
with the others, that they were called Asteroids. Since the 
-vear 1845 thirty-one more have been discovered, so that there 


ASTRONOMY 


330 


are now known to be no fewer than thirtv-five asteroids, or minor 
planets, between the orbits of Mars and Jupiter. 

1225. The Minor Planets. —The following is a catalogue 
of the minor planets at present known, arranged in the order 
of their discovery, together with the other known planets of oui 
solar system : 


Ntme and Number by which 
th< Minor Planets are'known. 

Date of Discovery. 

Names of Discoverers. 

& UN. 


* 

M ERCURY. 

Y ENU8. 

The Earth. 

Mars. 

1. Ceres. 

1801..Jan. 1. 

Piazzi, of Sicily. 

Ol hers, of Bremen. 

2. Pallas. 

1802..March 28... 

8. Juno. 

1804.. Sept. 1. 

Harding. 

Olbers. 

4. Vesta. 

1807..March 29... 

5 Astrea. 

1845. .Dec. 8. 

Iiencke, of Germany. 

Hencke. 

6. Hebe. 

1847.. July 1. 

7. Iris. 

1847.. An trust 13... 

Hind, of London. 

8. Flora. 

1847.. Oct. 18. 

Hind. 

9. Metis... 

1S48..April 26 .... 

Graham, of Ireland. 

10. llygeia. 

1849..April 12 .... 

De Gasparis, of Naples 

11. Parthenope. 

12. Clio. 

1S50. .May 11. 

1S50. .Sept. 13. 

De Gasparis. 

Hind. 

18. Egeria. 

1S50. .Nov. 2. 

De Gasparis. 

Ilind. 

14. Irene. 

1S51. .May 19. 

15. Eunomia. 

1851..duly 29. 

De Gasparis. 

De Gasparis. 

16. Psyche. 

1852.. March 17... 

17. Thetis. 

1852. .April 17 .... 

Luther, of Germany. 

IS. Melpomene. 

1852. .June 25. 

Hind. 

19. Fortuna. 

1S52..August 22... 

Hind. 

20. Massilia. 

1S52. .Sept. 19. 

De Gasparis. 

Goldschmidt, Paris. 

21. Lutetia. 

1852..Nov. 15. ... 

22. Calliope. 

1S52. .Nov. 16. 

Hind. 

28. Thalia. 

1852.. Dec. 15. 

Ilind. 

24. Themis. 

1&53..April 5. 

De Gasparis. 

Chacornac, of Marseilles, 

25. Phoesea. 

1S53..April 6. 

26. Proserpina. 

27 Euterpe....___.... 

1S53. .May 5. 

1853. .Nov. 8. 

Luther. 

Hind. 

28. Bellona. 

1S54.. March 1.... 

Luther. 

29. Amphitrite. 

1S54..March 1.... 

Marth cf London. 

80 Urania ..... 

1854..July 22. 

Hind. 

81. Euphrosyne. 

1S54.. Sept. 1. 

Ferguson, of Washington, 

82 Pomona ... 

1854..Oct. 28. 

Goldschmidt. 

88 Polhymnia. 

1854..Oct. 28. 

Chacornac. 

84 * /. . 

1S55.. April 14. 

Chacornac. 


1S55. .April 27. 

Jupiter. 

Saturn. 

T iRANTTft .... 

1181. 

Sir William Herschel. 

Neptune. 

1846..Sept.23...-j 

Dr. Galle, of Berlin, by d’reo 
tion of Le Vender, of l aris. 


*• To the last two asteroids in the list no names have as yet been eriven. 
It is proper to be observed that the asteroids are frequently known bettfiJ 
by their numbers than by their names. Thus Q represents Polity muia, 
and Q Calliope, Ac. 





































































340 


NATURAL PHILOSOPHY. 


1226. The name planet properly means 
difference be- a wandering star, and was given to this 
tween a planet class ol the heavenly bodies because they 
* 7 *“ a 8tai. are constantly moving, while those bodies 
which are called fixed stars preserve their relative posi¬ 
tions. The planets may likewise be distinguished from 
the fixed stars by the eye by their steady light, while 
the fixed stars, on the contrary, appear to twinkle. 

1227. The sun, the moon, the planets, and the fixed stars, 
which appear to us so small, are supposed to be large worlds, 
of’,arious sizes, and at different but immense distances from us. 
The reason that they appear to us so small is, that on account of 
their immense distances they are seen under a small angle of vision. 

What univer - 1228. It has been stated, in the early pages 

sal 7 <m keeps of this book; that every portion of matter is at- 

theplanets tracted by every other portion, and that the 
ii«./ other hea- J J . r 

venly bodies in force of the attraction depends upon the quantity 
places? of matter and the distance. As attraction is 
mutual, we find that all of the heavenly bodies attract the 
earth, and the earth likewise attracts all of the heavenly bodies. 
It has been proved that a body when actuated by several forces 
will be influenced by each one, and will move in a direction 
oeiwem them. It is so with the heavenly bodies; each one of 
thorn is attracted by every other one; and these attractions are 
so nicely balanced by creative wisdom, that, instead of rushing 
together in one mass, they are caused to move in regular paths 
(called orbits) around a central body, which, being attracted in 
d/jfevent directions by the bodies which revolve around it, will 
itseT revolve around the centre of gravity of the system. Thus, 
the sun is the centre of what is called the solar system, and the 
placets revolve around it in different times, at different dis¬ 
tances, and with different velocities. 

1229. The paths or courses in which the 
by*an % orbit? 1 l^ anets niove around the sun are called 
their orbits. 


ASTRONOMY. \ 

All of the heavenly bodies move in conic sections,* namely, the 
circle, the ellipse, the parabola and the hyperbola. 

What is meant 1230. In obedience to the universal law of 
a year! gravitation, the planets revolve around the 
sun as the centre of their system ; and the time that each 
one takes to perform an entire revolution is called its year. 
Thus, the planet Mercury revolves around the sun in 87 
of our days; hence a year on that planet is equal to 87 
days. The planet Venus revolves around the sun in 224 
days ; that is, therefore, the length of the year of that 
planet. Our earth revolves around the sun in about ^65 
days and 6 hours. Our year, therefore, is of that length. 

1231. The length of time that each planet takes in perform* 
ing its revolution around the sun, or, in other words, the length 
of the year on each planet, is as follows. (The fractional 
\-parts of the day are omitted.) In the same connexion will also 
be found the mean distance of each planet from the sun, and 
the time of revolution around its axis, or, in other words the 
length of the day on each. 



LengOi of the Year in 
Days. 

Mean distance from 
the Sun 

in millions of Miles. 

Length of the 
Day in Hours 
and Mir. ’U-s. 

M nROURY.. . 

87 

867 

24 5 

V snus. 

224 

3<\ 

23 2, 

Earth. 

365 

95 

24 00' 

Mars . 

6S6 

145 

24 89' 

1. Ores. . 

1,6S0 




2. Pallas. 

1,638 




3. Juno . 

1,592 




4. Vosta . 

1,325 




5. Astrea . 






6. lie be . 






7. Iris . 










About 266 


9. Metis . 


Between 1,400 




10. Hygeia . 

f 

and 2,100 




11. Partbenope . 





13. Etruria . 






14. Irene . 






15. Euiiomia. 






16. Psyche. 

1,885 J 





* Conic sections are curvilinear figures, so called because they can <1*1 
be formed by cutting a cone in certain directions. If a eont be cut per¬ 
pendicular to its axis, the surface cut will be a circle. If cut oblique to 
the axis, the surface cut will be an ellipse. If cut parallel to the slope U 
the cone, the section will be a parabola, if cut parallel to the axes, ti e 
section will be an hyperbola. 






































NATCJKAL PHILOSOPHY. 


342 



Length of the Year 
in Days. 

Mean Distance from 
the Sun in millions 
of Miles. 

Length of tbs 
Day In Homs 
and Minnies 

17. Thetis . 

1,480 I 




IS. Melpomene . 

1.269 




1ft. Fortuna. 

1,396 




20. Manilla. 

1,359 


About 266 


21. Lutetia. 

1,387 



22. Calliope. 

1,815 

1.571 




23 Thalia . 




24. Themis. 

2,037 




25 Piioesea. 




26. Proserpina. 




27. Kuterpe. 




28. Bellona . 




29. Amphitrite. 




8l). Crania . 




81. Knphroxyne ... 




32. Pomona ... 




83. Polliymnia . 




84 i 

t Unnamed . 




oD. ) 

Jupiter. 

4.332 

494 

9 55' 

Saturn.>. 

10.759 

9u6 

10 16' 

U RANU8.... 

80.6S6 

1,824 

2,856 

NRPTnNK. 

60,126 







The sun turns on its axis in about 25 days and 10 hours. 


Give an ac¬ 
count of 
Mode's law. 


1232. There is a very remarkable law, dis¬ 
covered by Professor Bode, founded, it is true, 
on no known mathematical principle, but which 
has been found to accord so exactly with other calculations, 
that it is recognized as Bode’s law for estimating the distances 
of the planets from the sun. Thus : 

Write the arithmetical progression, 

0, 3, 6, 12, 24, 48, 96, 192, 384. 

To each of the series add 4, and we have the sums, 

4, 7, 10, 16, 28, 52, 100, 196, 388, 
which will represent very nearly the comparative distance of 
each planet. Now, the distance of the earth from the sun is 
95 millions of miles, and as that distance is represented in the 
progression by 10, it follows that the distance of Mercury is 
of 95 millions, of Venus t 7 q , &c. 

What led to 1233. It is to be observed, however, that before 
the discovery the discovery of the minor planets, there was a 
of the minor very remarkable interval between the planets 
planets? Mars and Jupiter, and that Bode’s law, which 
emned to accord with the distance of all the other planets, 




































ASTRONOMY. 


34 :* 


appeared here tc fail in us application. Kepler had suspected 
that an undiscovered planet existed in the interval; but it was 
not certainly known until a number of distinguished observers 
assembled at Lilienthal, in Saxony, in 1800, who resolved to 
direct their observations especially to that part of the heavens 
where the unknown planet was supposed to be. The result of 
the labors of these observers, and others who have followed 
them, has been the discovery of the thirty-five minor planets, 
all situated between the planets Mars and Jupiter. But these 
What opinion minor planets are so small, and their paths or 

has been conjectured 
one large and resplen- 
planets? dent orb, which, by the operation of some un¬ 
known cause, has exploded and formed the minor planets that 
revolve in orbits very near that of the original planet. 

1234. Of these thirty-five small bodies, which are quite invisible 
without the aid of a good telescope, ten were discovered by Mr. 
Hind, of Mr. Bishop’s private observatory, Regent’s Park, London; 
seven by De Gasparis, of Naples; three by Chacornac, at Marseilles; 
three by Luther, at B ;1 k, Germany; two by Olbers, of Bremen ; two 
by Hencke, of Drie^wi, Germany; two by Goldschmidt, at Paris; 
and one each by Piazzi, of Palermo; Harding, of Lilienthal, Ger¬ 
many ; Graham, at Mr. Cooper’s private observatory, Markree 
Castle, Ireland ; Marth, of London ; and Ferguson, of Washington. 


nan oeenjonn- orbits vary so little, that it 
ed in relation ,, x jLl . . ,, » , 

to the minor that the Y or, § 1 nal] y formed 


^ ^ 1235. The paths or orbits of the planets 

shape of the * re not exactly circular, but elliptical. 
orbits of the They are, therefore, sometimes nearer to 
planets? (;} ie gun t p an ^ others. The mean distance 
is the medium between thoir greatest and least distance. 
Those planets which are nearer to the sun than the 
earth are called inferior planets, because their orbits are 
within that of the earth; and those which are further 
from the sun are called superior planets, because their 
orbits are outside that of the earth. 


Give the rela~ 1236. The relative size of the sun, the 

*moon, ^ moon and the larger planets, as expressed by 

and primary the length of their diameters, is as follows * 
planets. 


NATURAL PHILOSOPHY. 


844 


Sun 

. . 882,000 

Mars . 

. . 4,100 

Moon . 

. . 2,153 

Jupiter 

. . 88,640 

Mercury 

. . 2,950 

Saturn 

. . 75,000 

Yenus . 

. . 7,800 

Uranus 

. . 34,500 

Earth . 

. . 7,912 

Neptune 

. . 37,500 

flow large are 

1237. The size of the minor 

planets has been 

he minor 

so variously estimated, that little reliance can be 


P !anets ? placed on the calculations. Some astronomers 
estimate them as a little over 1000 miles, while others place 
them much below that standard. Vesta has been described as 
presenting a pure white light; Juno, of a reddish tinge, and 
with a cloudy atmosphere ; Pallas is also stated as having a 
dense, cloudy atmosphere; and Ceres, as of a ruddy color. 
These four undergo various changes in appearance, and but 
little is known of any of them, except their distance and time 
of revolution. 

Explain 1238. Fig. 182 is a representation of the com- 
Fig. 182. parative size of the larger planets. 


Fig. 182. 



.Sir J. F. W. Hersehel gives the following illustration of the com 
parative size and distance of the bodies of the solar system. “ On 
a well-levelled field place a globe two feet in diameter, to represen: 
the Sun ; Mercury will be represented by a grain of mustard-seed, 
on the circumference of a circle 164 feet in diameter for its orbit ; 
Venus, a pea, on a circle 284 feet in diameter; the Earth, also a 
{.ea, on a circle of 460 feet, Mars, a rather large pin’s head, on a 





ASTRONOMY. 


845 


circle of 654 feet; Juno, Ceres, Vesta, and Palas, grains of sand, 
in orbits of from 1,000 to 1,200 feet; Jnpiter, a moderate-sized 
orange, in a circle nearly half a mile in diameter; Saturn, a small 
orange, on a circle of four-fifths of a mile; Uranus, a full-sized 
cherry, or small plum, upon the circumference of a circle more than 
a mile and a half’; and Neptune, a good-sized plum, on a circle 
about two miles and a half in diameter. 

“To imitate the motions of the planets in the above-mentioned 
orbits, Mercury must describe its own diameter in 41 seconds; 
Venus, in 4 minutes and 14 seconds; the Earth, in 7 minutes; 
Mars, in 4 minutos and 48 seconds; Jupiter, in 2 hours, 56 minutes; 
Saturn, in 3 hours, 13 minutes; Uranus, in 12 hours, 16 minutes; 
and Neptune, in 3 hours, 30 minutes.” 


~^yWhat is the 
Ecliptic , and 
why is it so 
called t 


1239. The Ecliptic is the apparent path 
of the sun, or the real path of the earth. 

It is called the ecliptic, because every 
eclijpse, whether of the sun or the moon, 


must be in or near it. 


1240. The Zodiac is a space or belt, six- 
Zodlac? ^ teen degrees broad, eight degrees each side 
of the ecliptic. 

It is called the zodiac from a Greek word, which sig¬ 
nifies an animal , because all the stars in the twelve 
parts into which the ancients divided it were formed 
into constellations, and most of the twelve constellatiuns 
were called after some animal. 


1241. Sir J. F. W. Uersohel, in his excellent treatise on As¬ 
tronomy, says: “ Uncouth figures and outlines of men and mon¬ 
sters are usually scribbled over celestial globes and maps, and 
serve, in a rude and barbarous way, to enable us to talk of groups 
of stars, or districts in the heavens, by names which, though $hsurd 
or puerile in their origin, have obtained a currency from which it 
would be difficult to dislodge them. In so far as they have really 
(as some have) any slight resemblance to the figures called up in 
imagination by a view of the more splendid ‘ constellations, they 
have a certain convenience; but as they are otherwise entirely ar¬ 
bitrary, and correspond to no natural subdivisions or groupings 
of the stars, astronomers treat them lightly, or altogether disregard 
them, except for briefly naming remarkable stars, as 4 Alpha LeonisJ 
4 Beta Scorpiii &c., by letters of the Greek alphabet attached to tr.em. 

“This disregard is neither supercilious nor causeless. The con¬ 
stellations seem to have been almost purposcb named and delineated 


846 


NATURAL PHILOSOPHY. 


to cause as much confusion and inconvenience as possible. In* 
numerable snakes twine through long and contorted areas of the 
heavens, where no memory can follow them; bears, lions, and 
fishes, large and small, northern and southern, confuse all nomen¬ 
clature, &c. A better system of constellations might have been a 
material help as an artificial memory.” 

What are the 1242. The zodiac is divided into twelve 

si ^ns of the signs, each sign containing thirty degrees of 

zodiac, and how , . , . . ® J _ . 

many degrees in tlle g reat celestial circle. The names oi these 

cac h ■ signs are sometimes given in Latin, and 

sometimes in English. They are as follows : 


Latin. English. 

(1) Aries, The Ram. 
'2) Taurus, The Bull. 
[3) Gemini, The Twins. 
(1) Cancer, The Crab. 
(5) Leo, The Lion. 
;' 6 ) Virgo, The Virgin, 


Latin. English. 

(7) Libra, The Balance. 

( 8 ) Scorpio, The Scorpion. 

(9) Sagittarius, The Archer. 

(10) Capricornus, The Goat. 

(11) Aquarius, The Water-bearer. 

(12) Pisces, The Pishes. 


1243. The signs of the zodiac and the various bodies of the 
solar system are often represented, in almanacs and astronomical 
works, by signs or characters. 

In the following list the characters of the planets, &c., aie 
icpresentcd. 

(?) The Sun. 0 The Earth. 9 Ceres. 

<L The Moon. Mars. $ Pallas. 

£ Mercury. g Vesta. % Jupiter. 

9 Venus. J Juno. ^ Saturn. 

¥ Uranus. 

1 he following characters represent the signs of the Zodiac. 

°f° Aries. SL Leo. t Sagittarius. 

8 Taurus. Virgo. V? Capricornus. 

n Gemins. Libra. xz Aquarius. 

S3 Cancer. iq Scorpio. x Pisces. 

Brom an inspection of Pig. 183 it appears that when the earth 



ASTmXOMT. 


Have the signs 
of the zodiac 
always remain¬ 
ed the same , 
and why l 


a* seen from the sud, is in any particular constellation, the sun 
as viewed from the earth, will appear in the opposite one. 

1244. The constellations of the zodiac do not 
now retain their original names. Each con¬ 
stellation is about 80 degrees eastward of the 
sign of the same name. For example, the con¬ 
stellation Aries is 30 degrees eastward of the sign Aries, and the 
constellation Taurus 80 degrees eastward of the sign Taurus, and 
so on. Thus the sign Aries lies in the constellation Pisces; the 
sign Taurus, in the constellation Aries; the sign Gemini, in the 
constellation Taurus, and so on. Hence the importance of dis¬ 
tinguishing between the signs of the zodiac and the constellations 
of the zodiac. The cause of the difference is the precession of 
the equinoxes, a phenomenon which will be explained in its proper 
connexion. 

Howa-e the 1245. The orbits of the other planets 

ylanets'situated aru inclined to that of the earth; or, in 

with respect to other words, they are not in the same 
that of the -i 

earth ? P lane ‘ 

Explain Fig- 183 represents an oblique view of the plane 
Eig. 183. of the ecliptic, the orbits of all the primary planets, 
and of the comet of 1680. That part of each orbit which is 
above the plane is shown by a white line; that which is below 
it, by a dark line. That part of the orbit of each planet where 
it crosses the ecliptic, or, in other words, where the white and 
dark lines in the figure meet, is called the node of the planet, 
from the Latin nadtts, a knot or tie. 

Explain 1246. Fig. 184 represents a section of the plane 
Fig. 184. of the ecliptic, showing the inclination of the orbits 
of the planets. As the zodiac extends only eight degrees on 
each side of the ecliptic, it appears from the figure that the 
orbits of some of the planets are wholly in the zodiac, whilo 
those of others rise above and descend below it. Thus the 
orbits of Juno, Ceres and Pallas, rise above, while those of all 
the other planets are confined to the zodiac. 


Fig. 183 


348 


NATURAL philosophy, 

































































































































































































































































ASTRONOMY. 


319 


l\7ien is 1247. When a planet or heavenly body 

heavenly oot.y ... y J 

said to be in any 13 m that part oi its orbit which appears to 

constellation ? be near an y particular constellation, it is said 

to be in that constellation. 


This, in Fig. 147, the comet of 1680 appears to approach the 
aun from the constellation Leo. 


What is meant 1248 - The perihelion* and aphelion* 
by the perihelion of a hea venly body express its situation with 

re S ard t0 the sun - When a bod y is noare3 ‘ 

gee, of a heavenly to the sun, it is said to be in its perihelion. 
fjoa - ' When furthest from the sun, it is said to 

be in its aphelion. 


1249. The earth is three millions of miles nearer to the 
sun in its perihelion than in its aphelion. 

The apogee * and perigee * of a heavenly body express 
its situation with regard to the earth. When the body is 
nearest to the earth, it is said to be in perigee ; -when it is 
furthest from the earth, it is said to be in apogee. 


-nr-, . 1250. The perihelia of the planets, as seen from 

<?r<? w e y le sun , are j n following signs of the zodiac, 
pen e ion anil narae jy ; Mercury in Gemini, Venus in Leo, the 
aphelion of the Eartl / in Cancer> Mars iri Pisce3> Vesta in Sagitta¬ 
rius, Juno in Taurus, Ceres in Leo, Pallas in Leo, 
Jupiter in Aries, Saturn in Cancer, Uranus in Virgo, and Neptune 
in Taurus. 

What is meant 1251. When a planet is so nearly on a 
^superior ° T bne with the earth and the sun as to pass 
conjunction and between them, it is said to be in its inferior 
vtanet ? 011 ° conjunction ; when behind the sun, it is said 


* Tho plural of Perihelion is Perihelia , and of Aphelion is Apheha. The 
vrerds perihelion, aphelion, apogee, and perigee , a,'9 derived li orn the tJreek 
f-. iguage, and have tho following meaning : 

Perihelion, near the sun 
Aphelion, from the sun. 

Perigee, near the earth. 

Apogee, from the earth 

30 


NATURAL PHILOSOPHY. 


$<50 


to be in its superior conjunction; bat when behind tht 
earth, it is said to be in opposition. 

1252. The axes of the planets, in their 
revolution around the sun, are not perpen¬ 
dicular to thur orbits, nor to the plane of the 
ecliptic, but are inclined in different degrees. 

1253. This is one of the most remarkable 
circumstances in the science of Astronomy, 
because it is the cause of the different seasons, 


What is the in¬ 
clination of the 
axes of the 
planets to the 
p lane of their 
oriit j l 

What causes 
the seasons ? 
What causes 
the differences 
in the length of 
the da i/s and 
niirhts l 


spring, summer, autumn and winter; and 


because it is also the cause of the difference in 
the length of the days and nights in the different parts of 
the world, and at the different seasons of the year. 

1254. The motion of the heavenly bodies is not uniform. 
They move with the greatest velocity when they are in 
perihelion , or in that part of their orbit which is nearest 
to the sun; and slowest when in aphelion. 

1255. It # \vas discovered by Kepler, and proved by 
Xewton, that if a line is drawn from the sun to either 
of the planets, this line 
passes over or describes 
equal areas in equal times. 

This line is called the ra¬ 
dius-vector. This is one of 
Kepler’s great laws. 

In Fig. 185, 
let S represent the 
sun, and E the earth, and the 
ellipse or oval, be the earth’s 
orbit, or path around the sun. 

By lines drawn from the sun 
a t S to the outer edge of the g . 
figurthe orbit is divided 


Explain 
Fig. 185. 








ASTKO.NO JUT. 


351 

into twelve ar^as of different shapes, bat each containing the 
same quantity of space. Thus, the spaces E S A, A S B, D S C, 
&c., are all supposed to be equal. Now, if the earth in the 
space of one month will move in its orbit from E to A, it will 
’n another month move from A to B, and in the third month 
from B to C, &c., and thus its radius vector will describe equal 
areas in equal times. 

The reason why the earth (or any other heavenly body) moves 
with a greater degree of velocity in its perihelion than in its 
aphelion may likewise be explained by the same figure. Thus : 

The earth, in its progress from F to L, being constantly urged 
forward by the sun’s attraction, must (as is the case with a fall¬ 
ing body) move with an accelerated motion. At L, the sun’s 
attraction becomes stronger, on account of the nearness of the 
earth; and consequently in its motion from L to E the earth 
will move with greater rapidity. At E, which is the perihelion 
of the earth, it acquires its greatest velocity. Let us now detain it 
at E, merely to consider the direction of the forces by which it 
is urged. If the sun’s attraction could be destroyed, the force 
which has carried it from L to E would carry it off in the dotted 
line from E to (x, which is a tangent to its orbit. But, while the 
earth has this tendency to move towards Gr, the sun’s attraction 
is continually operating with a tendency to carry it to S. Now, 
when a body is urged by two forces, it will move between them, 
but, as the sun’s attraction is constantly exerted, the direction 
of the earth’s motion will not be in a straight line, the diagonal 
of one large parallelogram, but through the diagonal of a num- 
bci of infinitely small parallelograms ; which, being united, form 
the curve line E A. 

It is thus seen that while the earth is moving from L to E the 
attraction of the sun is stronger than in any other part of its 
orbit, and will cause the earth to move rapidly. But in its 
motion fiom E to A, from A to B, from B to C, and from 
C to F, the attraction of the sun, operating in an opposite direc¬ 
tion, -will Cause its motion from the sun to be retarded, until, at 
F. the direction of its motion is reversed, and it begins again to 


NATURAL PHILOSOPHY. 




approach the sun. Thus it appears that in its passage from the 
perihelion to the aphelion the motion of the earth, as well as 
that of all the heavenly bodies, must be constantly retarded, 
while in moving from their aphelion to perihelion it is con 
stantly accelerated, and at their perihelion the velocity will be 
the greatest. The earth, therefore, is about seven da} r s longer 
in performing the aphelion part of its orbit than in traversing 
he perihelion part; and the revolution of all the other planets, 
being the result of the same cause, is affected in the same man¬ 
ner as that of the earth. 


“A 


1256. The other two great laws dis¬ 
covered by Kepler, on which the discoveries 
of Newton, as well as the whole modern 
theory of the planets, are based, are — 


What are the 
three laws of 
Kepler ? 


1257. (1.) That the planets do not move in circles, 
but in ellipses, of which the sun is in one of the foci. 

1258. (2.) In the motion of the planets, the squares 
of the times of revolution are as the cubes of the mean 


distances from the sun. 


It was by this law that, in the want of other means, the 
distance of the planet Uranus from the sun was estimated. 
How much nearer 1259. The earth is about three millions 

VfirTmmmef of milcs nearer to t,,e sun in "' inte1 ' than 

than in the icin- in summer. The heat of summer, tliere- 

ter? [Be careful f ore can p e on ]y partially affected by 
not to he caught ’ , f f J 

in this question ] the distance ot the earth from the sun. 


The sun is nearest to the earth in the summer of the southern 
hemisphere, and the heat is more intense there than in corres¬ 
ponding latitudes of the north. This is due to the greater 
amount of land in the northern hemisphere, which by its radi¬ 
ating power diffuses the heat more equally. 


When is the heat 1260 ‘ 0n a ° count of tlle inclination ot 
of the sun the the earth’s axis, the rays of the sun fall 
t/rea*-** 4 9 more or less obliquely on different parts 


ASTRONOMY. 


353 


of the earth’s surface at different seasons of the year 
The heat is always the greatest when the sun’s rays fall 
vertically ; and the more obliquely they fall, the fewer 
of them fall on any given space. 

This is the reason why the days are hottest in summer, although 
the earth is further from the sun at that time. 

Explain 1261. Fig. 186 represents the manner in which 
tig. 186 ra y g t k e gun f a q U p 0n earth in summer and 

in winter. The north pole of the earth, at all seasons, constantly 
points to the north star N ; and, when the earth is nearest to the 
sun, the rays from the sun fall as indicated by W in the figure; 
and, as their direction is very oblique, and they have a large? 

Kg. m 



portion of the atmosphere to traverse, much of their power i? 
lost. Hence we have cold weather when the earth is nearest te 
the sun. But when the earth is in aphelion the rays fall almosl 
vertically or perpendicularly, as represented by S in the figure 
and, although the earth is then nearly three millions of miles 
further from the sun, the heat is greatest, because the rays fall 
more directly, and have a less portion of the atmosphere to 
traverse. 

This may be more familiarly explained by comparing summer 
rays to a ball or stone thrown directly at an object, so as to 
80 * 








354 


NATURAL PHILOSOPHY. 


strike it witn xll its force; and winter rays to the same ball o? 

stone thrown obliquely, so as merely to graze the object. 

Why is it cooler 1262. For a similar reason we find, even in 

early in the summer, that early in the morning and late in 

morntng than . , 

in the middle the afternoon it is much cooler than at noon, 

of the day ? because the sun then shines more obliquely. 

The heat is generally the greatest at about three o’clock in the 

afternoon; because the earth retains its heat for some length of 

time, and the additional heat it is constantly receiving from the 

sun causes an elevation of temperature, even after the rays 

begin to fall more obliquely. 


1263. It is the same cause which occasions 
the variety of climate in different parts of the 
earth. The sun always shines in a direction 
nearly perpendicular, or vertical, on the equator, 
and with different degrees of obliquity on the other parts of the 
earth. For this reason, the greatest degree of heat prevails at 
the equator during the whole year. The further any place is 
situated from the equator, the more obliquely will the rays fall 
at different seasons of the year, and, consequently, the greater 
will be the difference in the temperature. 


What causes the 
different cli¬ 
mates in differ¬ 
ent parts of the 
world 1 


What places will 


1264. If the axis of the earth were perpen- 
nave the coolest dicular to its orbit, those parts of the earth 
temperature? which lie under the equator would be constantly 
opposite to the sun; and as, in that case, the sun would, at all 
times of the year, be vertical to those places equally distant from 
both poles, so the light and heat of the sun would be dispersed 
witn perfect uniformity towards each pole; we should have no 
variety of seasons ; day and night would be of the same length, 
and the heat of the sun would be of the same intensity every 
day throughout the year. 


What effects are 
produced hy the 
inclination of 
the earth's axis? 


1265. It is, therefore, as has been stated 
owing to the inclination of the earth!x 
axis that we have the agreeabU variety 


ASTRONOMY. 


355 


if the seasons , days and nights of different lengths, 
and that wisely-ordered variety of climate which causes 
so great a variety of productions, and which has afford¬ 
ed so powerful a stimulus to human industry. 

12GG. The wisdom of Providence is frequently displayed in appar¬ 
ent inconsistencies. Thus, the very circumstance which, to the 
short-sighted philosopher, appears to have thrown an insurmountable 
barrier between the scattered portions of the human race, has been 
wisely ordered to establish an interchange of blessings, and to bring 
the ends of the earth in communion. Were the same productions 
found in every region of the earth, the stimulus to exertion would 
be weakened, and the wide field of human labor would be greatly 
diminished. It is our mutual wants which bind us together. 


1267. In order to understand the illustration of the causes of 
the seasons, &c., it is necessary to have some knowledge of the 
circles which, are drawn on the artificial representations of the 
earth. It is to be remembered that all >f these circles are 
wholly imaginary; that is, that there are on the earth itself no 
such circles or lines. They are drawn on maps merely for the 
purpose of illustration. 

Explain 1268. Fig. 187 represents the earth. N S is the 
lig. 187. ax [ Sj or imaginary line, around which it daily turns; 
N is the north pole, S is the south pole. Fig . 187 . 

These poles, it will be seen, aie the 
extremities of the axis N S. CD 
represents the equator, which is a cir¬ 
cle around the earth, at an equal dis¬ 
tance from each pole. The curved 
lines proceeding from N to S are me¬ 
ridians. They are all circles sur¬ 
rounding the earth, and passing through 
the poles. These meridians may be multiplied at pleasure. 

The lines E F, I K, L M, and G H, are designed to represent 
circles all of them parallel to the equator, and for this reason 
they are called parallels of latitude. These also may be mul 
tiplied at pleasure. 

Bui in the figure these lines, which are parallel to the equa tor 










$56 


NATURAL PHILOSOPHY. 


and which are at a certain distance from it, have a different 
name, derived from the manner in which the sun’s rays fall on 
the surface of the earth. 

Thus the circle I K, 23£ degrees from the equator, is called 
the tropic of Cancer, and the circle L M is called the tropic of 
Capricorn. The circle E F is called the Arctic Circle. It 
represents the limit of perpetual day when it is summer in the 
northern hemisphere, and of perpetual night when it is winter. 

On the 21st of March the rays of the sun fall vertically on 
the equator, and on each succeeding day on places a little to the 
north, until the 21st of June, when they fall vertically or places 
23^ degrees north of the equator. Their vertical direction then 
turns back again towards the equator, where the rays again fall 
vertically on the 23d of September, and on the succeeding days 
a little to the south, until the 21st of December, when they fall 
vertically on the places 23^ south of the equator. Their verti¬ 
cal direction then again turns towards the equator Hence the 
circles I K and L M are called the troj/ics of Cancer and Cap¬ 
ricorn. The word tropic is derived from a word which signifies 
to turn. The tropics, therefore, are the boundaries of the sun’s 
apparent path north and south of the equator, or the lines at 
which the sun turns back. 

The circle G H is the Antarctic Circle, and represents tho 
limit of perpetual day and night in the southern hemisphere. 
The line L K represents the circle of the ecliptic, which, as has 
already been stated, is the apparent path of the sun, or the rea. 
path of the earth. This circle, although it is generally drawn 
on the terrestrial globe, is, in reality, a circle in the heavens; 
and differs from the zodiac only in its width, — the zodiac ex¬ 
tending eight degrees on each side of the ecliptic. 

Erplain 1269. Fig. 188 represents the manner in which the 
. ig. 188. gun shines on the earth in different parts of its orbit, 
or, in other words, the cause of the change in the seasons. S 
represents the sun, and the dotted oval, or ellipse, ABC D, the 
arbit of the earth. The outer circle represents the zodiac. 


AS1JS0N0MY. 


357 


the position of the twelve signs or constellations. On the 21st 
of June, when the earth is at D, the whole northern polar region 
is continually in the light of the sun. As it turns on its axis, 
therefore, it will be day to all the parts which are exposed to 
the light of the sun. But, as the whole of the Antarctic circle 
is within the line of perpetual darkness, the sun can shine on no 
part of it. It will, therefore, be constant night to all places 
within that circle. As the whole of the Arctic circle is within 


Fig. 188. 



he line of perpetual light, no part of that circle will be turned 
from the sun while the earth turns on its axis. To all places, 
therefore, within the Arctic circle, it will be constant day. 

On the 22d of September, when the earth is at C, its axis is 
neither inclined to nor from the sun, but is sidewise; and, of 
course, while one-half of the earth, from pole to pole, is enlight 
tmed, the other half is in darkness, as would be the case if its 
axis were perpeudieular to the plane of its orbit; and it is this 




NATURAL PlIIUaOPHY. 


808 


which causes the days and nights of this season of the year to 
be of equai length. 

On the 23d of December the earth has progressed in its orbit 
to B, which causes the whole space within the northern polar 
circle to be continually in darkness, and more of that part of th* 
earth north of the equator to be in the shade than in the ligh^ 
of the sun. Hence, on the 21st of December, at all places north 
of the equator the days are shorter than the nights, and at all 
places south of the equator the days are longer than the nights 
Hence, also, within the Arctic circle it is uninterrupted night, 
the sun not shining at all; and within the Antarctic circle it is 
uninterrupted day. the sun shining all the time. 

On the 20th of March, the earth has advanced still further, and 
is at A, which causes its axis, and the length of the days and 
nights, to be the same as on the 20th of September.^^ 

Wh a t is meant 1^70. Broin the explanation of figure 198, 
by the Equinoxes it appears that there are two parts of its orbit 
and the Sol- in which the days and nights are equal all ovei 
the earth. These points are in the sign of 
Aries and Libra, which are therefore called the equinoxes 
Aries is the vernal (or spring) equinox, and Libra the autumna? 
equinox. 

1271. There are also two other points, called solstices, because 
the sun appears to stand at the same height in the heavens in 
the middle of the day for several days. These points are in the 
signs Cancer and Capricorn. Cancer is called the summer sol¬ 
stice, and Capricorn the winter solstice. 

1272. Day and night are caused by the rota¬ 
tion of the earth on its axis every 24 houis. 
It is day to that side of the earth which is 
towards the sun, and night to the opposite side. 
The length of the days is in proportion to the 
inclination of the axis of the earth towards the sun. It may be seen, 
by the above figure, that in summer the axis is most inclined 
towards the sun, and then the days are the longest. As the north 


How are day 
and night caus¬ 
ed , and what is 
the reason of the 
difference in 
their length ? 


ASTKONOMT. 


359 


pole becomes less inclined, the days shorten, till on the 21st of De¬ 
cember it is inclined 23J- degrees from the sun, when the day., 
are the shortest. Thus, as the earth progresses in its orbit, after 
the days are the shortest, it changes its inclination towards the 
sun, till it is again inclined as in the longest days in the summer. 
Which of the 1273. As the difference in the length of the 

greatest ^differ- and the ni S llts » and tlie change of the 

ence in its sea- seasons, &c., on the earth, is caused by the in* 
sons ■ clination of the earth’s axis, it follows that all 

the planets whose axes are inclined must experience the same 
vicissitude, and that it must be in proportion to the degree of 
the inclination of their axes. As the axis of the planet Jupiter 
is nearly perpendicular to its orbit, it follows that there can be 
little variation in the length of the days and little change in the 
seasons of that planet. 

1274. There can be little doubt that the sun, the planets, stars, 
&c., are all of them inhabited; and, although it may be thought 
that some of them, on account of their immense distance from the 
eun, experience a great want of light and heat, while others are so 
near, and the heat consequently so great, that water cannot remain 
on them in a fluid state, yet, as we see, even on our own earth, that 
creatures of different natures live in different elements,— as, for 
instance, fishes in water, animals in air, &c.,— creative wisdom could, 
undoubtedly, adapt the being to its situation, and with as little 
exertion of power form a race whose nature should be adapted to 
the nearest or the most remote of the heavenly bodies, as was re¬ 
quired to adapt the fowls to the air, or the fishes to the sea. 


WhatiUheSun, 1275 - ° F ™ E S™-The Sun i 3 a 
end what is its spherical body, situated near the centre ot 
eiameter ? gravity of the system of planets of which 

our earth is one. 


Hjtv much lar^ 1276. Its diameter is 882,000 English 
u the earth than m ii eSj w hich is equal to 100 diameters of 
{Answer care- the earth; and, as spheres are to each 
fully.] other in the proportion of the cube of their 

respective diameters, therefore his cubic magnitude must 
exceed that of the earth one million of times. It revolver 


NATUKAL PHILOSOPHY. 


m 

around its axis in 25 days and 8 hours. This has been 
ascertained by means of several dark spots which have 
been seen with telescopes on its surface. 

1277. Sir ¥m. Herschel supposed the spots on the 
eun to be the dark body of the sun, seen through open¬ 
ings in the luminous atmosphere which surrounds him. 

1278. It is probable that the sun,* like all the other 
heavenly bodies (excepting,' perhaps, comets), is in¬ 
habited by beings whose nature is adapted to their 
peculiar circumstances. 

1279. Many theories have been advanced with regard 
to the nature of the sun. By some it has been regarded 
as an immense ball of fire; but the theory which seems 
most in accordance with facts is, that the light and heat 
-are communicated from a luminous atmosphere, or at¬ 
mosphere of flame, which surrounds the sun, at a con¬ 
siderable distance above the surface. 

What is the zo- 1280. The zodiacal light is a singular phe- 
diacal light , and nomenon, accompanying the sun. It is a faint 
light which often appears !x> stream up from 
the sun a little after sunset and before sunrise. It appears 
nearly in the form of a cone, its sides being somewhat curved 
and generally but ill defined. It extends often from 50° to 100° 
in the heavens, .and always nearly in the direction of the plane 
of the ecliptic. It is most distinct about the beginning of March, 
but is constantly visible in the torrid zone. The cause of this 
phenomenon is not known. 

1281. The sun, as viewed from the different planets, appears 
of different sizes according to their respective distances. Fig. 
489 affords a comparative^ view of his apparent magnitude, as 
seen from all except the last twenty of the minor planets. 


* In almanacs the sun is usually represented by a small circle, with th% 
face of a man in it, thus : ® 


ASTliONOMY 


361 


Fig. 189. 



Apparent Magnitude of the Sun as seen from the Planets 


VI 

























3t)2 NATURAL PHILOSOPHY. 


Describe the 
planet Mer¬ 
cury. 

being lost in 


1282. Op Mercuri —Mercury is tbe 
nearest planet to tbe sun, and is seldom seen; 
because bis vicinity to the sun occasions bia 
the brilliancy of the sun’s -ays. 


, r 1283. The heat of this planet is so great 

How many f ° 

seas are there that water cannot exist there, except m a 

on the planet state of vapor, and metals would be melted 
Mercury ? 1 

The intensity of the sun’s heat, which is in 

a same proportion as its light, is seven times greater ir v 

Mercury than on the earth, so that water there would be 

^u-rried off in the shape of steam; for, by experiments made 

with a thermometer, it appears that a heat seven times 

greater than that of the sun’s beams in summer will make 

1284. Mercury, although in appearance 
only a small star, emits a bright white light, 
by which it may be recognized when seen. 
It appears a little before the sun rises, and 
again a little after sunset; but, as its angular distance 
from the sun never exceeds twenty-three degrees, it is 
never to be seen longer than one hour and fifty minutes 
after sunset, nor longer than that time before the sun rises. 


water boil. 

How late at 
night may 
Mercury be 
seen ? 


How does Mer- 1285. When viewed through a good tele- 

cury appear scope, Mercury appears with all the various 
when seen 11 . J 11 

through a phases, or increase and decrease of light, with 

telescope ? which we view the moon, except that it never 

appears quite full, because its enlightened side is turned 
directly towards the earth only when the planet is so near 
the sun as to be lost to our sight in its beams. Like that 
of the moon, the crescent or enlightened side of Mercury is 
always towards the sun. The time of its ro.ah >u on ite 
axis has been estimated at about 24 lumit, 


ASTRONOMY. 


803 


Describe the 1286. Of Venus. —Venus, the second 

planet Venus. p] anet j n or( | er f rom th e &UI1) j g neares t to 

the earth, and on that account appears to be the largest 
and most beautiful of all the planets. During a part of 
the year it rises before the sun, and it is then called the 
morning star ; during another part of the year it rises after 
the sun, and it is then called the evening star. The heat 
and light at Venus are nearly double what they are at the 
earth. 


1287. By the ancient poets Venus was called Phosphor, or Luci¬ 
fer, when it appeared to the west of the sun, at which time it is 
morning star, and ushers in the light of day ; and Hesperus , or 
Vesper , when eastward of the sun, or evening star. 

Why is Venus 1288. Venus, like Mercury, presents to us 

never seen late a ll the appearances of increase a*»d decrease 
at night ? p .. . 1 . 0 , 

ot light common to the moon, bpots are also 

sometimes seen on its surface, like those on the sun. By 
reason of the, great brilliancy of this planet, it may some¬ 
times be seen even in the day-time by the naked eye. But 
t is never seen late at night, because its angular distance 
from the sun never exceeds forty-five degrees. In the 
absence of the moon it will cast a shadow behind an opaque 
body. 

1289. Both Mercury and Venus sometimes 
pass directly between the sun and the earth. 
As their illuminated surface is towards the sun, 
their dark side is presented to the earth, and they appear 
like dark spots on the sun’s disk. This is railed the 
transit of these planets. 


What is meant 
l y the transit 
of a planet ? 


1290. The reason why we cannot sec the stars and planets in 
the day-time is, that their light is so faint compared with the 
light of the sun reflected by our atmosphere. 

1291. Of tiie Earth. — The Earth on 
which we live is the next planet in the so’ar 


Describe the 
Kcrth as a 
pl-tntt. 


NATUKAL PHILOSOPHY. 


364 


jystem, in the order of distance, to Venus. It is a large 
globe or ball, nearly eight thousand miles in diameter, and 
about twenty-five thousand miles in circumference. It is 
known to be round, — first, because it casts a circular 
shadow, which is seen on the moon during an eclipse; 
secondly , because the upper parts of distant objects on 
its surface can be seen at the greatest distance; thirdly , 
it has been circumnavigated. It is situated in the midst 
of the heavenly bodies which we see around us at night, 
and forms one of the number of those bodies; and it 
belongs to that system which, having the sun for its centre, 
and being influenced by its attraction, is called the solar 
system. 


How much It is not a perfect sphere, but its figure is 

longer is the ^hat 0 f an Mate spheroid, the equatorial 
volar than the _ 1 . 1 

equatorial diameter being about twenty-six miles longer 

dimneter of the than its polar diameter. 

earthl [Think . r , 

before you It is attended by one moon, the diameter 

sycak.] 0 f w hi c h j s about two thousand miles. Its 


mean distance from the earth is about 240,000 miles, and 
it turns on its axis in precisely the same time that it per¬ 
forms its revolution round the earth; namely, in twenty- 
seven days and seven hours. 

^Describe the 1292. The earth, when viewed from the 
earth as a moon, exhibits precisely the same phases that 
moon. the moon j oes t0 us? k ut j n opposite order. 

When the moon is full to us, the earth will be dark to the 
inhabitants * of the moon; and when the moon is dark to 
us, the earth will be full to them. The earth appears to 
them about thirteen times larger than the moon does to us. 


* This observation should be qualified by the condition that the moon is 
inhabited. Although there is abundant reason for the belief that the 
planets are “ the green abodes of life” there are many reasons to b<'i : evv 
U.uJ the moon. iH its present stale, is neither inhabited nor habitable 


ASTRONOMY. 


365 


As the moon, however, always presents nearly the same 
side to the earth, there is one-half of the moon which we 
never see, and from which the earth cannot be seen. 


1203. As this book may possibly incite the inquiry how it is th.it 
the astronomer is able to measure the size and distances of those 
immense bodies the consideration of which forms the subject of 
Astronomy, the process will here be described by which the diam¬ 
eter of the earth may be ascertained. 

1294. All circles, as has already been stated, are divided into 3G0 
degr es, and, by means of instruments prepared for the purpose, 
the r unber of degrees in any arc or part of a circle can be correctly 
ascertained. Let us now suppose that an observer, standing upon 
any fixed point, should notice the position of a particular star, — the 
north or polar star, for instance. Let him then advance from his 
station, and travel towards the north, until he has brought the star 
exactly one degree higher over his head. Let him then measure the 
distance over which he has travelled between the two points of 
observation, and that distance will be exactly the length of one 
degree of the earth’s circumference. Let him multiply that dis¬ 
tance by 3G0, and it will give him the circumference of the earth. 
Having thus found the circumference, the diameter may readily be 
found by the common rules of arithmetic 

This calculation is based on the supposition that the earth is a 
perfect sphere, which is not the case, the equatorial diameter being 
about twenty-six miles longer than the polar. But it is sufficiently 
near the truth for the present purpose. The design of this work 
not admitting rigid mathematical demonstrations, this instance of 
the commencement of a calculation is given merely to show that 
what the astronomer and the mathematician tell us, wonderful as 
it may appear, is neither bare assertion nor unfounded conjecture. 


What motions 1295. It has been stated that the earth re- 

haoe the inhabit- yolves upon its axis every day. Now, as the 

ants of 'he earth eart j l a b ou t 25,000 miles in circumference. 
on the earth as a 

pJanet? See , it follows that the inhabitants of the equator 
a/so, No. 1296. are carr jed around this whole distance in about 
twenty-four hours,, and every hour they are thus carried through 
space in the direction of the diurnal motion of the earth at the 
rate of ^th of 25,000 miles, which is more than 1000 miles in 
an hour. 

1296. Hut this is not all. Every inhabitant travels with the 
earth through its immense orbit, the diameter of which is about 


NATURAL PHILOSOPHY. 




lions of miles every year. This will give him, at the same time, 
«a motion of more than 68 000 miles in an hour in a different 
direction. If the question be asked, why each individual is not 
sensible of these tremendously rapid motions, the answer is, 
that no one ever knew what it is to be without them. We can¬ 
not be sensible that we have moved without feeling our motion, 
as when in a boat a current takes us in one direction, while a 
gentle wind carries us, at the same time, in another direction 
It is only when our progress is arrested by obstacles of some 
kind that we can perceive the difference between a s«.ate ol 
motion and a state of rest. 


What would 
be the coJise- 
/uence if the 
earth should 
revolve on its 
axis once in 
an hour 1 


1297. The rapid motion of a thousand miles in 
an hour is not sufficient to overcome the centri¬ 
petal force caused by gravity; but, if the earth 
should revolve around its axis seventeen times in 
a day, instead of once, all bodies at the equator 
would be lifted up, and the attraction of gravita¬ 


tion would be counterbalanced, if not wholly overcome. 


1298. Certain irregularities in the orbit of the earth have 
been noticed by astronomers, which show that it is deviating 
from its elliptical form, and approaching that of a circle. In 
this fact, it has been thought, might be seen the seeds of decay. 
But Laplace has demonstrated that these irregularities proceed 
from causes which, in the lapse of immensely long periods, 
counterbalance each other, and give the assurance that there is 
no other limit to the present order of the universe, than the will 
of its great Creator. 


Describe the 1299. Of Mars. — Next to the earth is 
planet Mars, the planet Mars. It is conspicuous for its 
fiery-red appearance, which is supposed by Sir John 
Hersohel* to be caused by the color of its soil. 


* Sir John Herschcl is the son of Sir William Herschel, the discovered 
ol lht> planet Uranus. 


/ 


ASiL- ^Lr-HY. 


i 


ilic degree of l it and light at Mars is less than halt 
of that received by the earth. 

1300. Of the Minor Planets.— It has already been men¬ 
tioned that between the < ’bits of Mars and Jupiter thirty-five 
small bodies have been discovered, which are called the minor 
planets. It is a remarkable fact, that before the discovery oi 
JBode’s law (see No. 1232) certain irregularities observed in the 
motions of the old planets induced some astronomers to sup¬ 
pose that a planet existed between the orbits of Mars and Jupi 
tet. The opinion has been advanced that these small bodies 
originally composed one larger one, which, by some unknown 
force or convulsion, burst asunder. This opinion is maintained 
with much ingenuity and plausibility by Sir David Brewster. 
(See Edin. Encyc ., art. Astronomy.) Dr. Brewster further 
supposes that the bursting of this planet may have occasioned 
the phenomena of meteoric atones; that is, stones which have 
fallen on the earth from the atmosphere. 

Describe the 1301. Of Ju pitjsr.—J upiter is the largest 
'planet Jupiter. pi ari<3 t 0 f the solar system, and the most bril¬ 
liant, except Venu3. The heat and light at Jupiter aix- 
about twenty-five times less than that at the earth. This 
planet is attended by four moons, or satellites, the shadows 
of some of which are occasionally visible upon his surface. 

1302. The distance of those satellites from the planet are 
two, four, six and twelve hundred thousand miles, nearly . 

The nearest revolves around the planet in less than two days; 
the next, in less than four days; the third, in less than eight 
days; and the fourth, in about sixteen days. 

These four moons must afford considerable light to the inhab¬ 
itants of the planet; for the nearest appears to them four timei 
the size of our moon, the second about the same size, the third 
somewhat less, and the fourth about one-third the diameter of 


our moon. 


NATURAL PHILOSOPHY 


36 


1303. As the axis of Jupiter is nearly perpendicular to it. 
orbit, it has no sensible change of seasons. 


What use has 
been made of 
the eclipses of 
Jupiter's satel¬ 
lites ? 


1304. The satellites of Jupiter often pass be¬ 
hind the body of the planet, and also into its 
shadow, and are eclipsed. These eclipses are of 
use in ascertaining the longitude of places on the 
earth. By these eclipses, also, it has been ascer¬ 
tained that light is about eight minutes in coming from the sun 
to the earth; for an eclipse of one of these satellites appears 
to us to take place sixteen minutes sooner when the earth is in 
that part of its orbit nearest Jupiter than when in the part 
furthest from that planet. Hence, light is sixteen minutes in 
crossing the earth’s orbit, and of course half of that time, oi 
eight minutes, in coming from the sun to the earth. 


What is the ap- 1305. When viewed through a telescope, 
vcarance of Ju- severa j belts or bands are distinctly seen, some- 
through a tele- times extending across his disk, and sometimes 
SC0 P e ^ interrupted and broken. They differ in dis¬ 

tance, position, and number. They are generally dark; but 
white ones have been seen. 


On account of the immense distance of Jupiter from the sun 
and also from Mercury, Venus, the Earth and Mars, observer? 
on Jupiter, with eyes like ours, can never see either of the above 
named planets, because they would always be immersed in tu'- 
sun’s rays. 

Describe the 1306. Of Saturn. — Saturn is the sec- 
planet Saturn. ond in size, and the last but two in dis¬ 
tance from the sun. The degree of heat and light at 
tins planet is eighty times less than that at the earth. 

How is Saturn 1307. Saturn is distinguished from the 

particularly other planets by being encompassed bv 
distinguished ,, , , . . * n v 

from the other three large luminous rings. 1 hey reflect 

planets? the sun’s light in the same manner as his 

moons. They are entirely detached from each other, and 


ASTRONOMY. 


369 

from the body of the planet. They turn on nearly the 
■same axis with the planet, and in nearly the same time 

1308. These rings move together around the planet, 
but are about three minutes longer in performing their 
revolution about him than Saturn is in revolving about 
his axis. The edge of these rings is constantly at right 
angles with the axis of the planet. Stars are said to 
have been seen between the rings, and also between the 
inner ring and the body of the planet. The breadth of 
the two outer rings is about 27,000 miles, and the dis¬ 
tance of the second ring from the planet is about 19,000 
miles. As they cast shadows on the planet, Sir Win 
Herschel thought them solid. 

1309. The surface of Saturn is sometimes diversified, 
like that of Jupiter, with spots and belts. Saturn has 
eight satellites, or moons, revolving around him at dif¬ 
ferent distances, and in various times, from less than 
one to eighty days. 

1310. Saturn may be known by his pale and steady light. 
rr he eight moons of Saturn revolve at different distances around 
the outer edge of his rings. Sir William Herschel saw them 
moving along it, like bright beads on a white string. They do 
not often suffer eclipse by passing into the shadow of the planet, 
because the ring is in an oblique direction. 

Describe the 1311. .Of Ukanus.—U rauus, the fourth 
planet Uranus, in size, is the most remote of all the old 
planets. It is scarcely visible to the naked eye. The 
light and heat at Uranus are about 360 times less tha 
that of the earth. 

1312. This planet was long known by the name of 
Herschel, the discoverer, who, in announcing his dis 
covery, named it the “ Georgium Sidus,” in honor «»1 
King George III. The name of Uranus was given t<* it 
by the continental astronomers. 


NATURAI PHILOSOPHY. 


37b* 


What is the %en- 
;ral law of the 
rotation of sat¬ 
ellites / 


It .'as formerly oonsidered a small s'ar, bit Sir W'm. 
Flers.ihel, in 1781, discovered, from its motion, that it 
is a planet. 

By how many 1313 ‘ Ul ' anus ia attended by six moons, 
moons is Uranus or satellites, all of which were discovered 
attended? by Sir Wm. Ilerschel, and all of them re¬ 
volve in orbits nearly perpendicular to that of the 
planet. Their motion is retrograde. 

1314. It appears to be a general law of sat¬ 
ellites, or moons, that tney turn on their axis 
in the same time in which they revolve around 
their primaries. On this account, the inhabit 
ants of secondary planets observe some singular appearances, 
which the inhabitants of primary planets do not. Those whe 
dwell on the side of a secondary planet next to the primary will 
always see that primary; while those who live on the opposite 
side will never see it. Those who always see the primary will 
see it constantly in very nearly the same place. For example, 
those who dwell near the edge of the moon’s disk will always 
see the earth near the horizon, and those in or near the centre 
will always see it directly or nearly overhead. Those who dwell 
in the moon’s south limb will see the earth to the northward , 
those in the north limb will see it to the southward; those in 
the east limb will see it to the westward ; while those in the 
west limb will see it to the eastward; and all will see it nearer 
the horizon in proportion to their own distance from the centre 
of the moon’s disk. Similar appearances are exhibited to the 
inhabitants of all secondary planets. These observations are 
predicated on the supposition that the moon is inhabited. But 
it is not generally believed that our moon is inhabited, or in its 
present condition fitted for the residence of any class of beings 
L315. It is a singular circumstance, that before the discovery < f 


ASTRONOMY. 


371 

JJr&mia soiiits d aturbanees and deviations were observed by astron 
omei*s in the motions of Jupiter and Saturn, which they could 
account for only on the supposition that these two planets were in 
fluenced by the attraction of some more remote and undiscovered 
planet. The discovery of Uranus completely verified their opinions, 
and .shows the extreme nicety with which astronomers observe the 
motions of planets. 

What led to the 1B1G Of Neptune. — The discovery of the 
discovery of the planet Neptune (named originally Le Verrier, 
plarut Neptune ? f rom discoverer, in 1846) is one of the greatest 
triumphs which the history of science records. As certain per¬ 
turbations of the movements of Saturn led astronomers to sus¬ 
pect the existence of a remoter planet, which suspicions were 
fully confirmed in the discovery of Uranus, so also, after the dis¬ 
covery of Uranus, certain irregularities were perceived in his 
motions, that led the distinguished astronomers of the day to the 
belief that even beyond the planet Uranus still another undis¬ 
covered planet existed, to rewal'd the labors of the discoverer. 
Accordingly Le Verrier, a young French astronomer, urged by 
his friend Atago, determined to devote himself to the attempi 
at discovery. With indefatigable industry he prepared new 
tables of planetary motions, from which he determined the pertur¬ 
bations of the planets Jupiter, Saturn, and Uranus, and as early 
as June, 1846, in a paper presented to the Academy of Sciences 
in Paris, he pointed out where the suspected planet would be 
on the 1st of January, 184 7. He subsequently determined the 
mass and the elements of the orbits of the planet, and that, too, be¬ 
fore it had been seen by a human eye. On the 18th of September 
of 1846, he wrote to his friend, M. Gralle, of Berlin, requesting 
him to direct his telescope to a certain point in the heavens, where 
he suspected the stranger to be. His friend complied with his 
request, and on the first evening of examination discovered a 
strange star of the eighth magnitude, which had not been laid down 
in any of the maps of that portion of the heavens. The follow¬ 
ing evening it was found to have moved in a direction and with a 
velocity very nearly like that which Le Verrier had pointed out. 
Che planet was found within less than one degree of the place 


372 


"NATI.'it \ l rm r.osovH v. 


where Le Verrier had located it. It was subsequently ascer¬ 
tained that a young English mathematician, Mr. Adams, oi 
Cambridge, had been engaged in the same computations, and 
had arrived at nearly the same results with Le Verrier. 

1317. What shall we say of science, then, that enables its devoted 
followers to reach out into space, and feel successfully in the dark 
for an object more than twenty-eight hundred millions of miles 
distant ? 

1318. In conclusion of this brief notice of the planets, a piate 
is here presented showing the relative appearance of the planets 
as viewed through a telescope. It will be observed that the 
planets Mercury ami Venus have similar phases to those of < ju 
moon. 


Fig 190 



Relative Telescopic appearance of the Planets. 


What is a 1319. Of Comets. — The word Comet is o > 
Comet ? rived from a Greek word, which means hair ; and 
this name is given to a numerous class of bodies, which occa¬ 
sionally visit and appear to belong to the solar system. These 
bodies seem to consist of a nucleus, attended with a lucid 
haze, sometimes resembling flowing hair ; from whence the 
name is derived. Some comets appear to consist wholly 
















ASTliONOMY. 


at triis hazy or hairy appearance, which is frequently called 
the tail of the comet. 


Fig. 191. 



Comet of 1811, one of the most brilliant of modern times. Period, 2888 

years. 

1320. In ancient times the appearance of comets was regard¬ 
ed with superstitious fear, in the belief that they were the fore¬ 
runners of some direful calamity. These fears have now been 
banished, and the comet is viewed as a constituent member of 
the system, governed by the same harmonious and unchanging 
laws which regulate and control a the other heavenly bodies. 

1321. The number of comets that have occasionally appeared 
within the limits of the solar system is variously stated from 350 
to 500. The paths or orbits of about 98 of these have been 
calculated from observation of the times at which they most 
nearly approached the sun; their distance from it and from the 
earth at those times; the direction of their movements, whether 
from cast to west, or from west to east; and the places in thf 

32 




374 


NATURAL PHILOSOPHY. 


starry sphere at which their orbits crossed that of the earth and 
their inclination to it. The result is, that, of these 98, 24 passed 
between the sun and Mercury, 33 passed between Mercury and 
Venus, 21 between Venus and the Earth, 16 between the Earth 
and Mars, 3 between Mars and Ceres, and 1 between Ceres and 
Jupiter: that 50 of these comets moved from east to west; that 
their orbits were inclined at every possible angle to that of the 
earth. The greater part of them ascended above the orbit of 
the earth when very near the sun; and some were observed to 
dash down from the upper regions of space, and, after turning 
round the sun, to mount again. 

, 1322. Comets, in their revolution, describe 

What is the. shape ’ 

of the orbits of long narrow ovals. They approach very near 
cornetsf the suu j n one 0 f the ends of these ovals, and 

when they are in the opposite end of the orbit their distance 
from the sun is immensely great. 


1323. The extreme nearness of approach to the sun gives to 
9 . comet, when in perihelion, a swiftness of motion prodigiously 
great. Newton calculated the velocity of the comet of 1680 to 
be 880,000 miles an hour. This comet was remarkable for its 
near approach to the sun, being no further than 580,000 miles 
from it, which is but little more than half the sun’s diametei 
Brydone calculated that the velocity of a comet which he ob¬ 
served at Palermo, in 1770, was at the rate of two millions and 
a half of miles in an hour. 


1324. The luminous stream, or tail, of a comet, follows it as 
it approaches the sun, and goes before it when the 3omet recedes 
from the sun. Newton, and some other astronomers, considered 
the tails of comets to be vapors, produced by the excessive heat 
of the sun. Others have supposed them to bo caused by a re¬ 
pulsive influence of the sun. Of whatever substance they may 
he, it is certain that it is very rare , because the stars may bo 
distinctly seen through it. 

1325 The tails of comets differ very greatly in length 


ASTRONOMY. 


t> 11 

and some are attended apparently by only a small cloudy 
lip-lit, while the length of the tail of'others has been esti¬ 
mated at from 50 to 80 millions of miles. 


Kg. 192 



fho t mot of 1680, observed by Newton. Rapidity of its motion around 
the sui: i million of miles in an hour. 

Lenf- of taii, 100 millions of miles Period, 600 years. It has nevot 
loapptu d 

1320. It has been argued that comets consist of very little 
riolid substance, because, although they sometimes approach very 
near to the other heavenly bodies, they appear to exert no sensi 
ble attn^ live force upon those bodies. It is said that in 1154 
the moon ,vas eclipsed by a comet. The comet, must, therefore, 
have been very near the earth (less than 240,000 miles); yet it 
produced ro sensible effect on the earth or the moon ; for it did 
not cause them to make any perceptible deviation from their 












NATURAL PHILOSOPHY 


i*76 


accustomed paths round the sun. It has been ascertained that 
comets are disturbed by the gravitating power of the planets ; 
but it does not appear that the planets are in like manner alfectc! 
by comets. 

Some comets have exhibited the appearance of two or mor* 5 
tails, and the great comet of 1744 had six 


Fig 193 



The great aoiuet of i7*4 



























AS'lltON >MY. 


377 


1327. Man}' comets escape observation because tbvy traverse 
that part of the heavens only which is above the horizon in the 
day-time. They are v therefore, lost in the brilliancy of the sun, 
and can be seen only when a total eclipse of the sun takes place 
Seneca, 60 years before the Christian Era, states that a larg« 
comet was actually observed very near the sun, during an eclipse. 

1328. Dr. Halley, Professor Encke and Gambart, are the first 
astronomers that ever successfully predicted the return of a 
comet. The periodical time of Halley’s comet is abemt 76 years. 
It appealed last in the fall of 1835, and presented different ap 


Fig. 194. 



uet. ms. 


ilalley’s eouict, as seen by Sir John HerscheJ, . - 7 ... .. 

flH^ngeable in its appearance First recognized by Hailey in 168 
riwd, 7fi years. 


32* 






natukal philosophy, 


<*578 

pearac ses from different points of observation. That of Encktf 
is abo- rt 1200 days ; that of Biela, about 6J years. This last 
rou>"‘ ippeared in 1832 and in 1838. 

Fig. 195. 



In W82 J ’"peri^: ?6 yZt? 12 ‘ h ’ 1835 KrSt 8600 by 

1329. Tbj comet of 1758, the return of which was predicted 
by Dr. Ha,ley, was regarded with great interest by astronomers, 
because i.r. return was predicted. But four revolutions before, 
in 1456, was looked upon with the utmost horror. Its long 
iail spread consternation over all Europe, already terrified by 
the rapid success of the Turkish arms. Pope Callixtus, on this 
occasion, ordered a prayer, in which both the comet and the 
Turks were included in one anathema. Scarcely a year or a 















astkojsomy. 


3::) 


month now elapses without the appearance of a comet in our 
system. But it is now known that they are bodies of such ex¬ 
treme rarity that our clouds are massive in comparison with 
them. They have no more density than the air under an ex- 
nausted receiver. Herschel saw stars of the 6th magnitude 
through a thickness of 30,000 miles of cometic matter. The 
number of comets in existence within the compass of the solar 
system is stated by some astronomers as over seven millions. 

1330. Fig. 194 represents Halley’s comet, as seen by Sir John 
Herschel, while Fig. 195 represents the same comet as seen only 
a few days before by Struve. 

1331. The Comet of 185G.— The following interesting details in 
relation to a comet expected in 1856 are given by Babinet, an em- 
.ment French astronomer. It is translated from tiie Courier des 
Etats Unis. 

“ This comet is one of the grandest of which historians make 
mention. Its period of revolution is about three hundred years. It 
was seen in the years 104, 392, 683, 975, 1264, and the last time in 
1556. Astronomers agreed in predicting its return in 1848; but it 
failed to appear, and continues to shine still unseen by us. Already 
the observatories began to be alarmed for the fate of their beautiful 
wandering star, when a learned calculator of Middlebourg, M. 
Bomme, reassured the astronomical world of the continued existence 
of the venerable and magnificent comet. 

“ Disquieted, as all other astronomers were, by the non-arrival 
of the comet at the expected time, M. Bomme, aided by the prepar- 
at >ry labors of Mr. Bind, has revised all the calculations and esti¬ 
mated all the actions of all the planets upon the comet for three 
hundred years of revolution. The result of this patient labor gives 
the arrival of the comet in August, 1858, with an uncertainty of 
two years, more or less ; so that from 1856 to 1860 we may expect 
the great comet which was the cause of the abdication of the Em¬ 
peror Charles V., in 1556. 

It is known that, partaking of the general superstition, which 
interpreted the appearance of a comet as the forerunner of some 
fatal event, Charles V. believed that this comet addressed its menaces 
particularly to him, as holding the first rank among sovereigns. The 
great and once wise but now wearied and shattered monarch, had 
been for some time the victim of cruel reverses. There were threat¬ 
ening indications in the political, if not in the physical horizon, of a 
8till grea ter tempest to come. He was left to cry in despair, '* For¬ 
tune abandons old men.’ The appearance of the blazing star seemed 
to him an admonition from Heaven that he must cease to be a sov¬ 
ereign il he would avoid a fatality from which one without author- 


3*0 


NATURAL PHILOSOPHY. 


ity might be spared. It is known that the emperor survived In* 
abdication but a little more than two years. 

“ Another comet, which passed near us in 1835, and which ba« 
appeared 25 times since the year 13 before the Christian Era, has 
been associated by the superstitious with many important event* 
which have occurred near the periods of its visitation. 

“ In 10GG, William the Conqueror landed in England at the head 
of a numerous army about the time that the comet appeared which 
now bears the name of Halley’s comet. The circumstance was 
regarded by the English as a prognostic of the victory of the Nor¬ 
mans. It infused universal terror into the minds of the people, and 
contributed not a little towards the submission of the country after 
the battle of Hastings, as it had served to discourage the soldiers 
of Harold before the combat. The comet is represented upon the 
famous tapestry of Bayeux, executed by Queen Matilda, the wife of 
the conqueror. 

“ This celebrated tapestry is preserved in the ancient episcopal 
palace at Bayeux. It represents the principal incidents, including 
the appearance of the comet, in the history of the conquest of Eng¬ 
land by William, Duke of Normandy. It is supposed to have been 
executed by Matilda, the conqueror's wife, or by the Empress Ma¬ 
tilda, daughter of Henry I. It consists of a linen web, 214 feet in 
length and 20 inches broad ; and is divided into 72 compartments, 
each having an inscription indicating its subject. The figures are 
all executed by the needle. 

“ The same comet, in 1451, threw terror among the Turks undei 
the command of Mahomet II., and into the ranks of the Christians 
during the terrible battle of Belgrade, in which forty thousand Mus¬ 
sulmans perished. The comet is described by historians of the time 
as ‘ immense, terrible, of enormous length, carrying in its train a 
tail which covered two celestial signs (GO degrees), and producing 
universal terror.’ Judging from this portrait, comets have singu¬ 
larly degenerated in our day. It will be remembered, however, that 
in 1811 there appeared a comet of great brilliancy, which irlspired 
some superstitious fears. Since that epoch science has noted nearly 
30 comets, which, with few exceptions, were visible only by the aid 
of the telescope. Kepler, when asked how many comets he thought 
there were in the heavens, answered, ‘ As many as there are fish in 
the sea.’ 

“ Thanks to the progress of astronomical science, these singular 
stars are no longer objects of terror. The theories of Newton. 
Halley, and their successors, have completely destroyed the imag¬ 
inary empire of comets. As respects their physical nature, it was 
for a long time believed that they were composed of a compact 
centre, surrounded by a luminous atmosphere. On this subject the 
opinion of M. Babinet, who must be regarded as good authority on 
such questions, is as follows : ‘ Comets cannot exercise any material 
influence upon our globe ; and the earth, should it traverse a comet 
in its entire breadth, w< uld perceive it no more than if it should jrosj 


ASTKONUilV. 


3b 1 


1 . cloud a hundred thousand millions of times lighter than our at¬ 
mosphere, and which could no more make its way through our as? 
than the slightest pufl of an ordinary bellows could make its way 
through an anvil.’ It would be difficult to find a comparison more 
reassuring.” # 


What are the 
Fixed Stars 
supposed lobe? 


1332. Of the Fixed Stars.— The Fixed 
Stars are all supposed to be immensely large 
bodies, like our own sun, shining by their 
jwn light, which they dispense to systems of their own 

How are the 1333. They are classed by their apparent 
fixed stars magnitudes, those of the sixth magnitude being 
classified? the smallest that can be seen by the naked 
eye. Stars which can be seen only by means of the telescope 


* Tan Co mkt of 1853. — Mr. Hind, in a letter to the London Times, gives 
the following particulars with regard to the comet which appeared during 
the year now closing (1853): 

“ The comet which has been so conspicuous during the last week was very 
favorably seen here on Saturday, and again on Sunday evening. On the 
latter occasion, allowing for the proximity of the comet to the horizon, and 
the strong glow of twilight, its nucleus was fully as bright as an average 
star of the first magnitude ; the tail extended about three degrees from the 
head. When viewed in the comet-seeker, the nucleus appeared of a bright 
gold color, and about half the diameter of the planet Jupiter, which was 
shining at the same time in the southern heavens, and could be readily com¬ 
pared with the comet. The tail proceeds directly from the head in a single 
stream, an l not, as sometimes remarked, in two branches. The distance of 
this body from the earth at 8 o’clock last evening, was 80,000,000 miles ; 
and hence it results, that the actual diameter of the bright nucleus was 
8000 miles, or about equal to that of the earth, while the tail had a real 
length of 4,500,000 miles, and a breadth of 250,000, which is rather over the 
distance separating the moon from the earth. It is usual to assume that 
the intensity of a comet’s light varies as the reciprocal of the products of 
the squares of the distance from the earth and sun; but the present one has 
undergone a far more rapid increase of brilliancy than would result from 
this hypothesis. The augmentation of light will go on till the 3rd of Sep¬ 
tember, and it will be worth while to look for the comet in the day-timo 
about that date ; for this purpose an equatorially mounted telescope will 
be required, and I would suggest the addition of a light green or red ghiss, 
‘o take off the great glare of sunlight, the instrument being adjusted to a 
cus on the planet Venus. This comet was discovered on the 10th of June, 
by Mr. Klinkenfues, of the Observatory at Gottingen, but was not bright 
enough to be seen without a telescope until about August 13. In a letter, 
copied into the Times a few days since, Sir William Hamilton hints at the 
possibility of this being the comet I had been expecting; but lavail myself 
ol the present opportunity of stating that such is not the case, the elements 
of tho orbits having no resemblance. Tho comet referred to will probably 
reappear between the years 1858 and 1801 ; and, if the perihelion passage 
takes place during the summer months, we may expect to see a bodv of fai 
tuore imposing aspect than the one at present visible.” 


382 


NATURAL PHU.'JSOFUY. 


are called telescopic stars. Th>y, also, are classified 
the classes reaching even to the seventeenth or twentieth 


magnitude. 


How many 133d. The number of the stars of the 

stars a,re there fj rs t magnitude is about twenty-four; of 
tcmfmagnl *e secolld magnitude, fifty; of the third. 
tude ? two hundred. The number of the smallest, 


visible without a telescope, is from twelve to fifteen 
thousand. 


How many of 1335 - Within a few years the distances 
the fixed stars of nine of the fixed stars have been calcu- 

have had their j a { e{ p This distance is so immense, that 
distances very . . . . . ■ 

nearly asce • light, travelling with the inconceivable 

tamed? velocity of nearly two hundred thousand 

miles in a second of time, from Sirius , is more than 
fourteen years in reaching the earth; from Arcturus, 
more than twenty-five years; and from the Pole Star, 
more than forty-eight years. 

1336. Tens of thousands of years must roll away before 
the most swiftly-flying of all the fixed stars can complete 
even a small fragment of its mighty orbit; but such has 
been the advance of science, that if a star move so slowly 
as to require five millions of years to complete its revo¬ 
lution, its motion could be perceived in one year ; and in 
ten years its velocity can be computed, and its period wifi 
become known in the lifetime of a single observer. 

Who first di- 1337. The stars are the fixed points to 
vided the stars which we must refer in observations of the 
)’wns? nSt€Ua ~ mot * ons °f the heavenly bodies. Hence 
the stars were grouped in the earliest ages, 
(but by whom we know not), numbered and divided into 
constellations, the names of which have survived the fall of 
empires 


ASTRONOMY. 


3S3 

Whatprolahly i338. It is generally supposed t\ at part, 

causes the dif- n ot«all, of the difference in the apparent 
Terence m the . \ . . 11 

apparent size magnitudes oi the stars is owing to the dif- 

of the stars t ference in their distance. 

1339. The distance of the stars, according to Sir J. 
flerschel, cannot be less than 19,200,000,000,000 miles. 
How much greater it really is, we know not, except in 
a few cases. 

1340. Although the stars generally appear fixed, they all have 
motion; hut their distance being so immensely great, a rapid mo¬ 
tion would not perceptibly change their relative situation in two or 
three thousand years. Some have been noticed alternately tc ap¬ 
pear and disappear. Several that were mentioned by ancient as¬ 
tronomers are not now to be seen; and some are now observed 
which were unknown to the ancients. 

1341. Many stars which appear single to the naked eye, when 
viewed through powerful telescopes, appear double, treble, and evei. 
quadruple. Some are subject to variation ir. their apparent magni¬ 
tude, at one time being of the second or diird, and at another of 
the fifth or sixth magnitude. 

What is the 1342. The Galaxy, or Milky Way, is a 
Galaxy? remarkably light, broad zone, visible in 
the heavens, passing from noith-east to south-west. It 
is known to consist of an immense number of stars, 
which, from their apparent nearness, cannot be distin¬ 
guished from each other by the naked eye. 

1343. Sir Wm. Herschel saw, in the course of a quarter of an 
hour, the astonishing number of 116,000 stars pass through the 
field of his telescope, while it was directed to the milky way. 

1344. The ancients, in reducing astronomy to a sci¬ 
ence, formed the stars into clusters , or constellations, to 
which they gave particular names. 

1345. The number of constellations among the ancients 
was about 50. The moderns have added about 50 more. 

1346. Our observations of the stars and nebulas are confined 
principally to those of the northern hemisphere. Of the coustella 
lions near the south pole we know but little., 


NATUltAL PHILOSOPHY. 


m 


What cjfect 1847. In determining the true place of any 
ias the atmu - 0 f t p e ce l e stial bodies, the refractive power of 
length of the the atmosphere must always be taken into 
ita y ■ consideration. This property of the atmo¬ 

sphere adds to the length of the days, by causing the sun 
to appear before it has actually risen, and by detaining its 
appearance after it has actually set. 


1348. On a celestial globe, the largest star in each constellation 
is usually designated by the first letter of the Greek alphabet, and 
the next largest by the second, &c. When the Greek alphabet is 
exhausted, the English alphabet, and then numbers, are used. 


Why are the 1349. The stars, and other heavenly bodies, 
stars never are never seen in their true situation, because 

seen m their t p e mo tion of light is progressive ; and. during 
true position ? ° 1 ® ° 

the time that light is coming to the earth, 

the earth is constantly in motion. In order, therefore, + o 

see a star, the telescope must be turned somewhat before 


the star, and in the direction in which the earth moves. 

What is meant 1350. Hence, a ray of light passing through 
hy the aberra- the centre of the telescope to the observer’s 
tion of light l e y e does co j nc jd e ^vith a direct line from 


his eye to the star, but makes an angle with it; and this is 
termed the aberration of light. 


What is the 1351. The daily rotation of the earth on its 
Polar Star / ax j g caugeg t p e w h 0 le sphere of the fixed 

stars, &c., to appear to move round the earth every twenty- 
four hours from east to west. To the inhabitants of the 


northern hemisphere, the immovable point on which the 
whole seems to turn is the Pole Star. To the inhabitants 


of the southern hemisphere there is another and a cor¬ 
responding point in the heavens. 

What is the 1352. Certain of the stars surrounding th*. 
circle of ye*-- north pole never set to us. These are in- 
i tion^nm ^r eluded in a circle, parallel with the equator 


ASTRONOMY. 


385 


perpetual oc- And in every part equally distant from the 
north pole star. This circle is called the 
circle of perpetual apparition. Others never rise to us. 
These are included in a circle equally distant from the 
south pole; and this is called the circle of perpetual or.- 
cultatwn. Some of the constellations of the southern 
hemisphere are represented as inimitably beautiful, par¬ 
ticularly the cross. 

What is par - 1353. The parallax of a heavenly body 
allaxt is the angular distance between the true 

and the apparent situation of the body. 

Describe 1354. In Fig. 196, A G B represents the earth 
Fig. 196. anc i Q the moon. To a spectator at A, the moon 


ng. m. d 



would appear at F; while to another, at B, the moon wouid 
appear at D ; but, to a third spectator, at G, the centre of tho 
earth, the moon would appear at E, which is the true situation. 
The distance from F to E is the parallax of the moon when 
viewed from A, and the distance from E to D is the parallax 
when viewed from B. 

1355. From this it appears that the situation of the heavenly 
bodies must always be calculated from the centre of the earth ; 
and the observer must always know the distance between the 
place of his observation and the centre of the earth, in order to 
make the necessary calculations to determine the true situation 
of the body. Allowance, also, must be made for the refraction 
of the atmosphere. ^ 

33 




366 


NATURAL PHILOSOPHY 


Describe the 3356. Of the Moon - -The Moon ix\ a 
Mftvn. secondary planet, revolving at'Hit the ea’tb 

in about twenty-seven days, seven hcuir. Its distanci 
from the earth is about 240.000 miles. It turns on ita 
axis in precisely the same time that it performs its rey 
olution about the earth. Consequently it always pre 
sents the same side to the earth; and as its apparen* 
diameter in different parts of its orbit is different, it fol 
1ow t s that it must he sometimes nearer to the earth that 
at others. 

135*7. The surface of the moon appears to be volcanic an? 
verv mountainous. Occasional volcanoes have been seen ir? 
action on the dark side. No heat has been detected in tht? 
moon’s rays, even when most powerfully concentrated, that wil 
affect the most delicate thermometer; and hence it has been in 
ferred that the heat is absorbed in traversing the upper region* 
of our atmosphere. 

What is one of the 1358. One of the most common errors 
most common errors w ph regard to the moon is that which as* 

mom°md d hoJhas eribe3 to ;t an influence over the weather. 
it l>een proved an Tables of the weather have been compared 
error ? with the lunar phases for a period of a hun¬ 

dred years, and over a thousand lunations, during which time 
about 491 new or full moons have been attended by a change 
of the weather, and 509 have not. 

1359. The moon is equally innocent of putrefaction, notwith¬ 
standing the popular belief that it hastens that process, especially 
'n fish. The same cause which produces dew causes moisture 
on substances exposed to it, and this moisture is the real cause 
of putrefaction. 

1360. Dr. Olbers, of Bremen, by a comparison of a great 
number of cases, arrived at the conclusion that the moon has no 
effect on insanity; although the popular belief is that the fits 
are aggravated or affected by the lunar phases. 


ASTIiONOMY. 


387 


What is the 1361. The force of gravity at the sur- 
demity of the f are 0 f the moon is about one-fifth that oi 
with that of the ^ earth ; lienee ten pounds on the earth 
earth? will be equal to two on the moon. The 

days and nights on the moon are each equal to fourteen 
of our days. The axis of the moon is perpendicular to 
its orbit, and therefore the moon can have no variety of 
seasons. The moon likewise has no atmosphere, and 
therefore it cannot be inhabited; for there can be no 
vegetation, no clouds, no ocean, no liquids, no light in 
dwellings, no twilight; in short, nothing that could fit 
it for the habitation of any order of beings with which 
we are acquainted. 

1362. In connexion with what has now been stated with regard 
to the moon and its volcanic appearances, it will be proper to notice 
the subject of aerolites , or meteoric stones; because, according to the 
opinion of some, they are of lunar origin. Three theories have 
been bioached with regard to them : 1st, that they are formed in 
the air, from materials existing there in a sublimated state ; 2d, 
that they are parts of an exploded planet; 3d, that they are thrown 
from the volcanoes in the moon. 

To the first of these theories there is a material objection in the 
fact that gases, when in contact, must mix, and gases necessary to 
form these substances cannot, therefore, remain in the air unmixed. 
To the second hypothesis it may be objected, that if they were 
arts of a broken planet they would probably be composed of more 
eterogeneous materials. But it is well known that all of them 
are composed of the same constituent parts, namely, sulphur, mag¬ 
nesia, manganese, iron, nickel, chromium, and, in one recorded 
instance only, charcoal. 

In favor of the third supposition, which refers them to a lunar 
origin, it may be remarked that a body thrown seventy miles from the 
moon would escape from the moon’s attraction ; and that a velocity 
six times greater than that of a cannon-ball would be sufficient to 
throw a body beyond the moon’s attraction. As terrestrial volcanoes 
have thrown bodies with this velocity, it is not improbable that 
lunar volcanoes may do the same. 

1363. The most obvious fact in relation to 
the moon is that its disc is constantly changing 
its appearance : sometimes only a semi-circular 
edge being illuminated, while the rest is dark 


What is the 
most obvious 
fact in rela¬ 
tion to the 
muon? 


388 


NATURAL PHILOSOPHY. 


hx another time, the whole surface appearing resplendent 
Tliis is caused by the relative position of the moon with 
regard to the sun and the earth. The moon is an opaque 
body, and shines only by the light of the sun. When, 
therefore, the moon is between the earth and the sun. it 
presents its dark side to the earth; while the side presented 
to the sun, and on which the sun shines, is invisible to the 
earth. But when the earth is between the sun and the 
moon, the illuminated side of the moon is visible at the 
earth. 

De$crih° 1364. In Fig. 197, let S be the sun, E the earth, 
Fig. 197. an( l A B 0 D the moon in different parts of hei 

Fig m 


c 



orbit When the moon is at A, its dark side will be towards 
the earth, its illuv? : nated part being always towards the sun. 
Hence the moon will appear to us as represented at a. But 
when it has advanced in its orbit to B, a small part of its 
illuminated side coming in sight, it appears as represented at b % 
and is said to be horned. When it arrives at C, one-half its 
illuminated side is visible, and it appears as at c. At C, and 
in the opposite point of its orbit, the moon is said to be in qvad - 
rv,ti<re. At D its appearance is as represented at d , and it is 
said to be gibbous. At E all the illuminated side is towards 
us, aud we have a full moon. During the other half of its 



ASfKONOMT. 


388 


revolution, less and less of its illuminated side is seen, til’ .1 
again becomes invisible at A. 

What is the 1365. The mean difference in the rising of the 
mean differ - moon, caused by its daily motion, is a little less 

rising of the than an hour * on account of the different 

moon from day angles formed with the horizon by different part*- 
to day ? 0 f ec liptic, it happens that for six or eight 

nights near the full moons of September and October the moon 
rises nearly as soon as the sun is set. As this is a great con¬ 
venience to the husbandman and the hunter, in- 
by the 1 Harvest asmuc ^ as affords them light to continue their 
and the Hunt - occupation, and, as it were, lengthens out their 

^h ^d^t) ^ 1S ca ^ e( ^ ^ mrvest moon, and the 
occur ? second the hunter's moon. These moons are 

always most beneficial when the moon’s ascending 
node is in or near Aries. 


1366. The following signs are used in our common almanacs 
to denote the different positions and phases of the moon. } or 
J) denote the moon in the first quadrature, that is, the quad¬ 
rature between change and full; C or ([ denotes the moon in 
the last quadrature, that is, the quadrature between full ar'd 
cnange. 9 denotes new moon ; O denotes full moon. 

1367. When viewed through a telescope, the surface of tbt, 
moon appears wonderfully diversified. Large dark spots, sup 
posed to be excavations, or valleys, are visible to the eye, 
some parts also appear more lucid than the general surface 
These are ascertained to be mountains, by the shadows which 
they cast. Maps of the moon’s surface have been drawn, on 
which most of these valley** and mountains are delineated, anc* 
names are given to them. Some of these excavations are 
thought to be four miles deep, and forty wide. A high ridge 
generally surrounds them, and often a mountain rises in the 
centre. These immense depressions probably very much re¬ 
semble what would be the appearance of the earth at the moon 

33* 


390 


NATURAL PHILOSOPHY. 


were all the seas and lakes dried up. Some of tlie mountains 
are supposed to be volcanic. 

What are the 1368. Of the Tides. — The tides are the 
Tides? regular rising and falling of the water of 

the ocean twice in about twenty-live hours. They are 
occasioned by the attraction of the moon upon the 
matter of the earth; and they are also affected by that 
of the sun. 

Explain 1369. Let M, Fig. 198, be the moon revolving in 
Fifj. 198. ber orbit; E, the earth covered with water; and S, 

Fig. 198. 



the &un. Now, the point of the earth’s surface, which is nearest 
to the moon, will gravitate towards it more, and the remoter 
point less, than the centre, inversely as the squares of their re¬ 
spective distances. The point A, therefore, tends away from 
the centie, and the centre tends away from the point B; and in 
each case the fluid surface must rise, and in nearly the same 
degree in both cases. The effect must be diminished in propoi- 
tioD to the distance from these points in any direction; and at 
the points C and D, ninety degrees distant, it ceases. But 
there the level of the waters must be lowered, because of the 
exhaustion at those places, caused by the overflow elsewhere. 
Thus the action of the moon causes the ocean to assume 
the form of a spheroid elongating it in the direction of the 
moon. 



LbTKONOMT. 


wn 


Thus any pa ' ,u,a 4 /lace, as A, while passing from under 
the moon till i\ comes under the moon again, has two tides. 
But the moon is consta -tly advancing in its orbit, so that the 
earth must a little more than complete its rotation before the 
place A comes under th\ moon. This causes high water at any 
place about fifty minuteu later each successive day. 

As the moon’s orbit raries but little from the ecliptic, 
the moon is nevei; more than 29° from the equator, and is 
generally much less. Ha nee the waters about the equator 
being nearer the moon, are more strongly attracted, and che 
tides are higher than tow rds the poles. 


1370. The sun attracts the waters as well as the moon. When 
the moon is at full or chang ■, being in the same line of direction, 
(see Fig. 198), the sun act* i with it; that is, the sun and moon 
tend to raise the tides at the same place, as seen in the figure. 
The tides are then very high, and are called spring tides. 
Explain Fig But wheii the moon is in its quarters, as in 
199. Fig. 199, the sun and moon being in lines at 


lg. 199. 



right angles tend to raLe tides at different places; namely 
the moon at C and D, and the sun- at A and B. Tides that are 
produced when the moon is in its quarters, are low, and are 
called neap tides. 

1371. There are so nr.j,ny natural difficulties to the free pro¬ 
gress of the tides, that the theory by which they are accounted 
for is, in fact, and necessarily, the most imperfect of all the 
theories connected with astronomy. It is, however, indisputable 
that the moon has an effect upon the tides, although it be not 




392 


NATURAL PHILOSOPHY. 


equally felt in all places, owing to the indentations of the coasj 
the obtructions of islands, continents, &c., which prevent the 
free motion of the waters. In narrow rivers the tides are fre¬ 
quently very high and sudden, from the resistance afforded by 
their banks to the free ingress of the water, whence what would 
otherwise be a tide, becomes an accumulation. It has been con¬ 
stantly observed, that the spring tides happen at the new and 
full moon, and the neap tides at the quarters. This circum 
stance is sufficient in itself to prove the connexion between the 
influence of the moon and the tides. 


What is an 
Eclipse 1 


1372. An Eclipse is a total or partial ob¬ 
scuration of one heavenly body by the interven¬ 
tion of another. 


The situation of the earth with regard to the 
eclipse of* the moon > or rather of the moon with regard to the 
sun or of the earth, occasions eclipses both of the sun and 
moon take place? moon# Those of the sun take place when the 
moon, passing between the sun and earth, intercepts his rays. 
Those of the moon take place when the earth, coming between 
the sun and moon, deprives the moon of his light. Hence, an 
eclipse of the sun can take place only when the moon changes, 
and an eclipse of the moon only when the moon fulls; for, at 
the time of an eclipse , either of the sun or the moon, the sun 
earth , and moon , must he in the same straight line. 


If the moon revolved around the earth in the 
not an eclipse at same P lane in which the earth revolves around 
evrry new and the sun, that is, in the ecliptic, it is plain that 
full moon. the sun would be eclipsed at every new moon, 
and the moon would be eclipsed at every full. For, at each of 
these times, these three bodies would be in the same straight 
line. But the moon’s orbit does not coincide with the ecliptic, 
but is inclined to it at an angle of about 5® 20'. Hence, since 
the apparent diameter of the sun is but about £ a degree, and 
that of the moon about the same, no eclipse will take place at 


ASTKONOMY. 


393 


new or full moon, unless the moon be within 1 a deg/ee of the 
ecliptic, that is, in or near one of its nodes. It is found that 
if the moon be within l(j£° of a node at time of change, it wil? 
be so near the ecliptic, that the sun will be more or less 
eclipsed* if within 12° at time of full, the moon will be more 
or less eclipsed. 

'Why are there 1373. It is obvious that the moon will be 
more eclipses of oftener within 16^° at the time of new moon, 

the sun than of t j ian w ithin 12° at the time of full; conse- 
the moon m a # 1 

given course of quently, there will be more eclipses of the sun 

years t than of the moon in a course of years. As the 

nodes commonly come between the sun and earth but twice in 

a year, and the moon’s orbit contains 360°, of which 16^°, the 

limit of solar eclipses, and 12°, the limit of lunar eclipses, are 

but small portions, it is plain there must be many new and full 

moons without any eclipses. 

Although there are more eclipses of the sun 
Explain Fig. ttan of the 

moon, yet more eclipses of the 
moon will be visible at a particular place, as 
Boston, in a course of years, than of the sun. Since the sun is 
very much larger than either the earth or moon, the shadow of 


Fig. 200. 



these bodies must always terminate in a point; that is, it must 
always be a cone. In Fig. 200, let S be the sun, m the moon, 
and E the earth. The sun constantly illuminates half the earth’s 
surface, that is, a hemisphere; and consequently it is visible to 
a ll in this hemisphere. But the moon’s shadow falls upon a 
part only of this hemisphere; and hence the sun appears 
eclipsed to a part only of those to whoa it is visible. Some* 
times, when the moon is at its greatest distance, its shadow, O 




NATURAL PHILOSOPHY. 


m, terminates before it reaches the earth. In eclipses of this 
kind, to an inhabitant directly under the point 0, the outermost 
edge of the sun’s disc is seen, forming a bright ring around the 
moon; from which circumstance these eclipses are called annu¬ 
lar , from annulus , a Latin word for ring. 

Besides the dark shadow of the moon, m 0, in which all the 
light of the sun is intercepted (in which case the eclipse is 
called total), there is another shadow, r C D S, distinct from 
the former, which is called the 'penumbra . Within this, only a 
part of the sun’s rays are intercepted, and the eclipse is called 
partial . If a person could pass, during an eclipse of the sun, 
from 0 to D, immediately on emerging from the dark shadow, 
0 m , he would see a small part of the sun; and would con¬ 
tinually see more and more till he arrived at D, where all 
shadow would cease, and the whole sun’s disc be visible. Ap 
pearances would be similar if he went from 0 to G. Hence 
the penumbra is less and less dark (because a less portion of 
the sun is eclipsed), in proportion as the spectator is more re¬ 
mote from O, and nearer G or D. Though the penumbra be 
continually increasing in diameter, according to its length, or 
the distance of the moon from the earth, still, under the most 
favorable circumstances, it falls on but about half of the illu¬ 
minated hemisphere of the earth. Hence, by half the inhab 
tants on this hemisphere, no eclipse will be seen. 


Explain Fig. 

joi. 


■"^74. Fig. 201 represents an eclipse of the 
moon. The instant the moon enters the earth’ 
shadow at x , it is deprived of the sun’s light 


Fig. 201. 











YblltO-NOMY. 




and is eclipsed to all in the unilluminated hemisphere of the 
earth. Hence, eclipses of the moon are visible to at least twice 
as many inhabitants as those of the sun can be; generally the 
proportion is much greater. Thus, the inhabitants at a par¬ 
ticular plac*\ as Boston, see more eclipses of the moon than of 
the sun. 

The reason why a lunar eclipse is visible to all to whom 
the moon at the time is visible, and a solar one is not so to all to 
whom the sun at the time is visible, may be seen from the 
nature of these eclipses. We speak of the sun’s being eclipsed; 
but, properly, it is the earth which is eclipsed. No change 
takes place in the sun; if there were, it would be seen by all 
to whom the sun is visible. The sun continues to diffuse its 
beams as freely and uniformly at such times as at others. But 
these beams are intercepted, and the earth is eclipsed only 
where the moon’s shadow falls, that is, on only a part of a 
hemisphere. In eclipses of the moon, that body ceases to 
receive light from the sun, and, consequently, ceases to reflect 
it to the earth. The moon undergoes a change in its appear¬ 
ance ; and, consequently, this change is visible at the same time 
to all to whom the moon is visible; that is, to a whole hemis¬ 
phere of the earth. 

1375. The earth’s shadow (like that of the moon) is encom¬ 
passed by a per-junora, C USD, which is faint at the edges 
towards R and S, but becomes darker towards F and G. The 
shadow of the earth is but little darker than the region of the 
penumbra next to it. Hence it is very difficult to determine 
the exact time when the moon passes from the penumbra into 
the shadow, and from the shadow into the penumbra; that is, 
when the eclipse begins and ends. But the beginning and end¬ 
ing of a solar eclipse may be determined almost instantaneously. 


What is meant 
by digits , as ap¬ 
plied to eclipses 
of the sun and 
od the moon ? 


1376. The diameters of the sun and moon 
are supposed to be divided into twelve equal 
parts, called digits. These bodies are saiu to 
have as many digits eclipsed as there are of 
those parts involved in darkness 


896 


NATURAL PHILOSOPHY. 


1377. There must be an eclipse of the sun at *>ften, at least, 
as the moon, being near one of its nodes, comes between the 
aun and the earth. 

The greatest number of both solar and lunar eclipses that can 
take place during the year is seven. The usual number is four, 
two solar and two lunar. 

1378. A total eclipse of the sun is a very remarkable phe¬ 
nomenon. 

June 16, 1806, a very remarkable total eclipse took place at 
Boston. The day was clear, and nothing occurred to prevent accu¬ 
rate observation of this interesting phenomenon. Several stars were 
visible ; the birds were greatly agitated ; a gloom spread over the 
landscape, and an indescribable sensation of fear or dread pervaded 
the breasts of those who gave themselves up to the simple effects of the 
phenomenon, without having their attention diverted by efforts of 
observation. The first gleam of light, contrasted with the previous 
darkness, seemed like the usual meridian day, and gave indescribable 
life and joy to the whole creation. A total eclipse of the sun can 
last but little more than three minutes. An annular eclipse of the 
sun is still more rare than a total one. 


1379. Of Time. —When time is calcu- 
ference between ^ ate( ^ by - the sun, it is called solar time, and 
the solar arid the the year a solar year; but when it is calcu- 
ndereal year . ] ate( j by the stars, it is called sidereal time, 
and the year a sidereal year. The sidereal year is 20 min¬ 
utes and 24 seconds longer than the solar year. 


1380. The solar year consists of 365 
days, 5 hours, 48 minutes, and 48 seconds; 
but our common reckoning gives 365 days 
only to the year. As the difference amounts 
to nearly a quarter of a day every year, it 
is usual every fourth year to add a day. Every fourth 
year the Romans reckoned the 6th of the calends of 
March , and the following day as one day ; which, on 
that account, they called bissextile, or twice the 6th day; 
whence we derive the name of bissextile for the leap year 


Which is the 
longer , a solar 
or a sidereal 
year, and by 
how much? 


ASTRONOMY. 


59 ? 


m <vhich we give to February, for the same reason, 29 
days every fourth year. 

1381. A solar year is measured from the time the earth 
sets out from a particular point in the ecliptic, as an equi¬ 
nox, or solstice, until it returns to the same point again. 
A sidereal year is measured by the time that the earth 
takes in making an entire revolution in its orbit; or, in 
other words, from the time that the sun takes to return into 
conjuction with any fixed star. 


What is thepre- 1382. Every equinox occurs at a point, 
cession of the 50" of a deg. of the great circle, preceding 
equinoxes ? the place of the equinox, 12 months before; 
and this is called the precession of the equinoxes. It is 
this circumstance which has caused the change in the situ¬ 
ation of the signs of the zodiac, of which mention has 
already been made. 

1383. The earth’s diurnal motion on an inclined axis, 
together with its annual revolution in an elliptic orbit, 
occasions so much complication in its motion as to pro¬ 
duce many irregularities; therefore, true equal time 
cannot be measured by the sun. A clock which is 
always perfectly correct will, in some parts of the year, 
be before the sun, and in other parts after it. There are 
When do the ^ut ^ our P er ^ 0( ^ s which the sun and $ 
sun and clock perfect clock will agree. These are the 
agree? 15 th 0 f April, the 15th of June, the lst.oi 

September, and the 24th of December. 

1384. The greatest difference between 
true and apparent time amounts to between 
sixteen and seventeen minutes. Tables of 
equation are constructed for the purpose c i 
pointing out and correcting these differences 
34 


What is the 
areatest dif¬ 
ference be¬ 
tween true 
and apparent 
lime ? 


398 


NATURAL PHILOSOPHY. 


between solar time and equal or mean time, tne denomina¬ 
tion given by astronomers to true time. 

1385. As it may be interesting to those whc have access to a 
celestial globe to know how to find any particular star or con¬ 
stellation, the following directions are subjoined. 

There is always to be seen, on a clear night, a beautiful clus* 
ter of seven brilliant stars, which belong to the constellation 
“ Ursa Major” or the -Great Bear. Some have supposed that 
they will aptly represent a plough; others say that they are 
more like a wagon and horses, the four stars representing the 
body of the wagon, and the other three the horses. Hence 
they are called by some the plough , and by others they are 
called Charles' wain, or wagon. 

Fig. 202 represents these seven stars; 
ah d g represent the four, and e z B 
the other three stars. Perhaps they 
may more properly be called a large, 
dippei of which e z B represent the 
handle. If a line be drawn through the 
stars 1 And a, and carried upwards, it 
will pas a little to the left, and nearly 
touch a ',iar represented in the figure by 
P. This is the polar star, or the north 
pole star; and the stars b and a, which 4^ 
appear to point to it, are called the pointers , because they 
appear to point to the polar star. 

The poltvr star shines with a steady and rather dead kind of 
light. It always appears in the same position, and the north 
pole of tb't earth always points to it at all seasons of the year. 
The other stars seem to move round it as a centre. As this 
star is always in the north, the cardinal points may at any time 
be found h r starlight. 

By thes stars we can also find any other star or eonsteJla- 
lion. 

Thus, if re conceive a line drawn from the star z , leaving B 


Fig. 202. 

r 

4 * 


k -f 4"^ 
/z e A 



ASTRONOMY. 


395 


a little to the left, it will pass through the very brilliant star A, 
By looking on a celestial globe for the star z , and supposing 
the line drawn on the globe, as we conceive it done on the 
heavens, we shall find the star and its name, which is Arcturus. 

Conceiving another line drawn through g and b and ex¬ 
pended some distance to the right, it will pass just abov another 
very brilliant star. On referring to the globe we Ltiu it to be 
/apella, or the goat. 

In this manner the student may beccme acquainted with the 
^pearancc of the whole heavens. 


Table 


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NATURAL PHILOSOPHY 



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NATURAL PHILOSOPHY. 


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NATURAL PHILOSOPHY. 


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NATURAL PHILOSOPHY 



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NATURAL PHILOSOPHY 


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ILLUSTRATIONS. 


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NATURAL PHILOSOPHY. 


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Fig. 197. 


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Fig. 198. 










ILLUSTRATIONS. 


447 


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Fig 201. 



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INDEX 


A. 


I narration of light.384 

“ spherical . . 247 

Accidental colors.252 

Achromatic.247 

Acid, carbonic.21 

Acid, sulphuric, effects of on 

water.-.187 

Acoustic paradox.177 

Acoustics.173 

“ definition of . . . 18 

Acoustic tubes.179 

Action. 45 

Action and reaction, illustration 

of.46 

Action, suspension of.85 

Aetynolite.21 

Aeriform, definition of . ... 19 

“ fluids.138 

Aeriform fluids compressed and 
expanded without limit . . . 139 
Aeriform fluids have no cohesive 

attraction.139 

Aeriform fluids have all the prop¬ 
erties of liquids.140 

Aeriform fluids have weight. . . 139 

Aeronaut, how he descends from 

a balloon.38 

Aerolites ..387 

Affinity, chemical.19, 27 

Agents.18 

“ imponderable.18 

*« ponderable....... 18 

Air.140 

Air, a bad conductor of heat . . 191 

Air, as an element.19 

Air-bladder of fishes.47 

Air-chamber.163 

Air, component parts of the . . 140 

281 note 

Air, compression of, caused by 
gravity.39 

88* 


Air, compressibility of the . 162 
Air, condensation of at surface ci 

the earth.140 

Air, condensed, experiments with 163 
Air contained in wood and water, 

experiments to show.16} 

Air diminishes upwards in dens¬ 
ity .. . . 146 

Air, elasticity of the . . . 142, 162 
Air, elasticity of the, experiments 

showing.100 

Air, effect of gravity on density of >8 
Air essential to animal life, ex¬ 
periment to prove.168 

Air essential to combustion, ex¬ 
periments to prove.16f 

Air, fluidity of.142 

Air, fluidity of, experiments show¬ 
ing .16!> 

Air, gravity of the, experiments 
illustrating .... . . . l.>7 

Air-gun.164 

Air, how a mechanical agent . .142 
“ impenetrability of . . . 22, 141 

“ inertia of.28, 143 

Air, inertia of, experiments show¬ 
ing .165 

Air, lightness of the.162 

“ materiality of the.162 

Air, miscellaneous experiments 

wAh.166 

Air necessary to animal life and 

to combustion.140 

Air, of what composed.20 

Air, pressure of the as the depth 162 
“ pressure of in all directions 162 
Air, pressure of the on a barom¬ 
eter .146 

Air, pressure of the on a square 

inch.141 

Air, pressure of the on the body 1 11 
Air, pressure of the preserves the 
liquid form of some bodies . .163 










































450 


INDEX. 


Air, prossure of the retards ebul¬ 
lition .168 

Air-pump.154 

Air-pump, experiments performed 

by the.157 

Air-pump of steam-engine . . .201 

Air-pump, the double.156 

Air, resistance of the .... 25, 38 
Air, resistance of the to a cannon¬ 
ball . 62 

Air, scales for weighing .... 160 
Air, two principles, properties of 139 

“ when heaviest.146 

Air, when the best conductor of 

sound.176 

Air, why not visible.140 


Albite 


20 


Alison, extract from.70 

w All’s well,” how far heard . .176 

Alumina.21 

Aluminum.20 

Ampere’s discoveries in electro¬ 
magnetism .309 

Ampere’s electro-magnetic appa¬ 
ratus .314 

Analysis of the motion of a fall¬ 
ing body.52 

Angle. 48 

Angles, how measured.48 

Angle of vision.219 

Angles of incidence and of reflec¬ 
tion . 48, 49, 216 

Angles, right, obtuse and acute . 48 

Animal electricity. 282 

Animals, sagaeity of.92 

Annealing.31 

Antimony.20 

“ not malleable.31 

Aphelion.349 

Apogee.349 


Apparatus for illustrating the 
tendency of a body to revolve 
around its shorter axis .... 61 
Apparition, circle of, perpetual . 385 


Apparitions, deceptive.225 

Aqueous humor. 237, 239 

Arago’s experiments on velocity 

of sound.176 

Arbor.81 


Archimedes’ boast to Hiero . . 95 
Archimedes, burning mirrors of. 228 
Archimedes discovers the method 
of ascertaining the specific grav¬ 


ity of bodies.127 note 

Archimedes, screw of.132 

Arc of a penluluui.101 

Axcturus . . . 399 


Aristotle’s opinion of the velocity 

of a falling body. 62 

Arsenic.20 

“ not malleable.3? 

Asteroids.33S 

Astraea.339 

Astronomy, definition of . 17, 18, 335 

Astronomers, distinguished . . . 336 

Astronomy, father of.336 

Atmosphere, weight of the . . . 141 

Atmospheric telegraph.331 

Attraction. 25, 26, 33 

capillary.Ill 

chemical.27 

kinds of.27 

law of falling bodies . 51 

mutual.34 

of all bodies.34 

of cohesion.27 

of gravitation .... 27 

of the earth.33 

on what dependent . . 34 

Attwood’s machine.52 

Augite.21 

Austral polarity.302 

Axes of the planets, inclination 

of.350 

Axis, exact sense of.81 

Axis, longer, a body revolving 

around.61 

Axis of motion.59 

Axis of the earth, effects of its 

inclination.354 

Axis of the earth, geological the¬ 
ory of.62 

Axis, what bodies revolve around 

an.59 

Axle.81 

Azote.20, 140 


B. 


Babbit’s metal.99 

Bain’s telegraph ....... 326 

Baker, the Connecticut.191 

Balance-wheel.104 

Balance.75 

Ballistic pendulum.63 

Balloon, how to descend from . . 38 
“ the pneumatic .... 161 
Ball, thrown in a horizontal di. 

rection..64 

Balia, force of, how estimated . 63 
Bands with one and two centres 

of motion.83 

Banks, Sir Joseph.190 

Barber’s Grammar of Elocution . 180 








































































INDEX. 


451 


Barium ..20 

Barometer .144 and note 

Barometer, the aneroid or porta¬ 
ble .145 

Barometer, the diagonal . . . 145 

Barometer, of the different states 

of the.148 

Barometer, greatest depression of 

the.147 

Barometer, its importance 146 note 

** rules of the.147 

“ the mercurial .... 145 

Base of a body.67 

Batteries, thermo-electric . . . 335 

“ galvanic.287 

Battering ram.105 

Battering ram, force of, how es¬ 
timated .105 

Battery, electrical.264 

Battery, Grove’s.293 

“ how discharged silently 265 
Battery of the electro-magnetic 

telegraph.321 

Battery, protected sulphate of 

copper . 293 

Battery, Smee’s.290 

“ sulphate of copper . .292 

Beam of light.213 

Belgrade, battle of, and the comet380 
Bellows, hydrostatic, how con¬ 
structed .119 

Bell, the diver’s or the diving . 150 

Bevelled Wheels.85 

Birds, bodies of.123 

“ how they fly.47 

muscular power of. ... 47 

Bismuth. 20 

“ not malleable. ... 31 

Bissextile, meaning of.396 

Black.252 

Black lead, uses of in overcom¬ 
ing friction.99 

Bladder-glass.159 

Bladder, inflated, why compress¬ 
ed in water..115 

Boats, how propelled.47 

Boats, on what principle they 

float.123 

Boats, motion in, why impercep¬ 
tible .26 

Bode’s law.342 

Bodies.18 

“ attraction of .... - . 33 
Bodies of drowned persons, why 
they sink and afterwards rise . 123 
Bodies, what are easily overset . 69 
what stand most firmly . 6S 


Bodies, what will rise and what 

will fall in air.40 

Body acted upon by three or more 

forces.57 

Body, parts of which move with 

greatest velocity.60 

Bodies, what ones will float and 

what sink in water.123 

Body, when it will fall.66 

Bohemia slate, formations of . . 23 
Bolt-head, and jar .... .167 

Bomme M.379 

Bones of a man’s arm, levers of 

third kind.77 

Borax.20 

Boreal polarity.302 

Bottle, effect of pressure of the 

sea upon.115 

Boyle.144 

Boynton’s, Dr., chart of materi¬ 
als which form granite .... 21 
Bramah’s hydrostatic press . . 121 
Brass, how made brittle .... 30 

Breadth.23 

Breaot-whsel.82, 83 

Brittleness.27, 30 

Brittleness, how acquired by iron, 
steel, copper and brass.... 30 

Bromine.2C 

Brooks, how formed.124 

Buckets of water-wheels .... 82 
Buckets of water, why heavier 
when lifted from the well . .126 
Bulk of a body, how ascertained 

from its weight.125 

Burdens, how made unequal . . 77 
Burning-glasses. 228, 235 

C. 

Cadmium.20 

Qilcium.20 

Calliope . ..339 

Caloric.187 

Calorimotor.297 

Camera obscura.219, 240 

Camera obscura, portable, how 

made.219 

Cannon-ball, greatest velocity 

that can be given to.63 

Cannon-ball, force of the resist¬ 
ance of the air to ..... . 62 

Cannon, how far heard.174? 

Caoutchouc, or India-rubber . . 30 
“ balls, elasticity of . 47 

Capillary attraction.Hi 

“ “ cause of . .Ill 



























































452 


INDEX. 


Capillar} tubes. Ill 

Capstan.80 

Capstan and windlass, difference 

between.80 

Carbon. 20 

Carbonate of lime.21 

Carbonate of magnesia.21 

Carbonic acid.21 

Carriages, high, why dangerous . 68 

Carronades.63 

Cartesian devil.162 

Cask, how burst by hydrostatic 

pressure . 120 note 

Cassegranian telescope .... 250 
Castors, why applied to legs of 

tables, &c...85 

Catoptrics.215 

Celestial bodies, true place of . 384 

Celsius’ thermometer.149 

Central forces.59 

Centre of gravity . . 57, 58, 59, 66 

Centre of gravity, illustrations 

of ... .66 note 

Centre of magnitude . . 58, 59, 66 

Centre of motion .... 58, 5y, 71 

Centre of sphericity.37 

Centre, what bodies revolve 

around a.59 

Centres.58 

Centrifugal force.59 

Centrifugal force, effect of on a 
body revolving around its longer 

axis.61 

Centrifugal force, to what propor¬ 
tioned .60 

Centrifugal force, where greatest 103 
“ meaning of .... 59 

Centripetal force.59 

“ meaning of .... 59 

Ceres.339 

Cerium.20 

Chain-pump.131 

Cnaises, tops of, toggle-joint . 97 

Chamfered.91 

Chantrey, the sculptor.191 

Charged, meaning of.261 

“ Charlemagne,” experiment on 

board of the.115 

Charles V. and the comet . . . 379 

Charles’ wain or wagon .... 398 

Chart of materials forming the 

crust of the earth.20 

Chemical affinity.19, 27 

Chemical attraction.27 

Chemical effects of light . . 256,257 

Chemical electricity.259 

Chemistry .19, 110 


Chimneys, glass, bow preserved 

from cracking. j92 

Chisels, on what principle cou 

structed .91 

Chlorine.20 

Chlorite.21 

Chord, musical, how produced . 182 

Choroid. 237, 240 

Chromatics..251 

Chromium.20 

Circle.48 

Circle of perpetual apparition . 385 

Circles.59 

Circles, circumference of, how di¬ 
vided . . 48, 365 

Circular motion.58 

Circular motion changed to rec¬ 
tilinear by cranks.8 * 

Circular motion, how caused . . 58 

Clay.21 

Climates, cause of.354 

Clock, before and after the sun . 397 

“ how regulated.102 

“ moving power of ... . 104 
Clock, periods when it agrees with 

the sun. . 397 

Clocks, why they go fastest in 

winter . 101 

Clock, what it is.102 

“ wheels of, their use . . . 102 
Clothing, cause of warmth of . . 189 
Clouds.24 


“ of what composed .... 186 


Cobalt. 20, 298 

“ not malleable.31 

Coffee-pots, why with wooden han¬ 
dles ..190 

Cogs.83, 84 

Cohesion, attraction of.27 

Cohesion, attraction of, its effects 

on watery particles.186 

Cold.185,192 

Cold, its effects on the density of 

bodies.192 

Colors.254 

“ accidental ....... 252 

Columbium.20 

Comets.372 

“ density of.379 


Comet, Halley’s, as seen by Sir 
John llerschel, and by Struve. 

377, 378, 379 

Comet, Halley’s, periodical time 

of.377 

Comets, how regarded former y . 373 
Comets in the solar system, num¬ 
ber of ... . . . , . 37^ 





































































INDEX. 


45b 


Comets, Kepler’s opinion of their 

number.380 

Comets, number of.373 

Comet of 1(380 375 

“ « 1744 37(3 

“ “ 1811.373 

Comet of 1853, Mr. Hind’s ac¬ 
count of the.381 

Comet of 185G.379 

Comets, orbits of.374 

Comets, return of, first predicted 
by iialley, Encke, and Hiela . 377 

Comets, tails of.374 

“ velocity of.37.. 

Common centre of gravity of two 

or more bodies.69 

Complex wheel-work.83 

Compound battery.290 

“ lever.75 

“ motion.55 

“ “ how produced . 54 

Compressibility. 27, 28, 29 

Concave mirrors.222 

“ v “ effects of . . . 225 
Concave mirrors, laws of reflec¬ 
tion from.227 

Concave mirrors, peculiar prop¬ 
erty of. 224 

Concave mirror, true focus of . . 224 

“ screw.94 

Concave surfaces, facts with re¬ 
gard to.236 

Condensation.140 

Condensed. 140 

Condenser.108 

“ of steam-engine . . . 200 
Condensing syringe . . . .156,163 

Conduction of heat.190 

Conductors of the galvanic fluid . 285 

“ . 258, 260 

“ of heat.189 

Cone.00 

Conic sections. 341 

Conjunction, inferior and supe¬ 
rior .349 

Connecticut baker.191 

Conservatory of arts and trades, 
how restored to perpendicular .193 
Constellations : . . . . . 383 

“ of the zodiac . . 347 

Oontractibility.28 

Converging rays.212 

Conversation in polar regions 
heard at great iistances . . .176 

Convex mirrors.222 

Convex mirrors, laws of reflection 
from . . . .226 


Convex mirrors, effects of . , . 224 

Convex screw.94 

Conv-ex surfaces, facts with regard 

to.235 

Copernicus.336 

Copper. .... 20 

Copper and tin, sonorous proper¬ 
ties of.30 

Copper, how made brittle ... 30 

Cords, tenacity of.32 

Cork, how deep it will sink . . . 123 
“ why lighter than lead . . 34 

Cornea. 237, 238 

Corpuscular theory of light . . .211 

Couronne des tasses.290 

Crank, dead point of.81 

Cranks.80 

Crown-wheel.84 

Crust of the earth, materials com¬ 
posing the ..20 

Crystalline humor, convexity, how 
increased or diminished . . . 241 
Crystalline humor, effect of when 

too round.242 

Crystalline lens.237 

Cup of Tantalus.133 

Cups, the Magdeburgh.157 

Current velocity of a, how meas¬ 
ured .130 

Curve of a projectile, on what de¬ 
pendent .64 

Curvilinear motion.61 

Cutting instruments.91 

Cylinder, definition of a ... . 79 
Cylinder, how made to roll up a 

slope.68 

Cylinder, wheel substituted for . 79 


D. 


Daguerreotype proofs.257 

Darkness produced by two rays 

of light.212 note 

Davies’ Treatise on Magnetism .316 
Day and night, cause of ... . 35H 
Days and nights, cause of differ¬ 
ence in length of.350 

Dead point of a crank.81 

Delisle’s thermometer.149 

Delphi, oracle of.180 

Demetrius Poiiorcctes . . . . 105 

Density. 27,28 

Density of air, effect of gravity 

on.38 

Depth of a well, how estimated . 53 

Descartes. 144 



































































454 


INDEX. 


Devil, the Cartesian.162 

Dew and fog,difference between. 150 
Dew, how produced ...... 150 

Diagonal.48 

“ of a parallelogram . . 55 

“ of a square.55 

Diallage.21 

Diameter.48 

Diameter, equatorial, how length¬ 
ened .. . 61 

Diameter, equatorial of the earth, 
longer than polar, and why . . 61 
Diameter of the earth, equatorial 

ami polar. 102 

Diameter of the earth, how ascer¬ 
tained ..365 

Didynium.20 

Digits ..395 

Dilatability.29 

Dionysius, ear of.178 

Dionysius, how he overheard his 

prisoners.178 

Dioptrics.230 

“ laws of.230 

Dipping of a magnet.303 

Dipping of a magnet, how reme¬ 
died ..303 

Direction.41 

“ line of.66 

Discharge, the jointed.264 

Dissolving views.246 

Distance at which a man is in¬ 
visible .220 

Distance, greatest which can be 

estimated.382 

Distances measured by velocity 

of sound.177 

Distillation.194 

Distilled water, why used as stand¬ 
ard of specific gravity . . . .123 

Diverging rays.212 

Divers, limit to the depth of . .115 

Diving bell, or diver’s bell . . . 150 

Divisibility.21 

“ extent of.23 

“ definition of ... . 23 
u Dodge,” how children .... 26 

Double action of the steam-engine 200 
Drowned persons, why they sink 

and afterwards rise.123 

Ductility.27,31 

Dynamics.17 

“ meaning of.18 

E. 

Earth . . 363 


Earth, a good conductor of sound I'r 6 
“ as viewed from the moon . 364 
M attraction of the .... 33 
“ centre of gravity of . 37 

Earth, consequences of a more 

rapid rotation of the.366 

Earth, constituent elements oftho 20 
Earth, crust of the, materials com¬ 
posing .29 

Earth, diameter of, how ascer¬ 
tained .365 

Earth, figure of the.364 

“ how known to be round . 364 
Earth, how much larger than any 

falling body.33 

Earth, motions of its inhabitants 365 
“ nearer the sun in winter . 352 
Earth, parts of which move most 

rapidly.61 

Earth, strata of the.20 

Earth, the principal reservoir of 

electricity.261 

Ebullition retarded by pressure 

of the air.168 

Echo.177 

“ why never heard at seb . . 178 

Eclipse.392 

“ annular.394 

Eclipses, greatest number of in a 

year.396 

Eclipse, lunar, to whom visible . 395 
“ solar, to whom visible . 395 

“ total of 1806 396 

Eclipses, why more of the sun 

than of the moon.393 

Eclipse, why not at every new and 

full moon.392 

Eclipse, partial.394 

“ total.394 

Ecliptic.345 

Egeria.339 

Ehrenborg’s microscopic observa¬ 
tions .23 

Elastic fluids.139 

Elasticity. 27, 29, 30 


“ of air. 


i( of gaseous bodies 

. . 30 

‘ of ivory. 


Electrical battery. 


“ bells. 


“ fire-alarm .... 


“ machine .... 

. . 266 

Electrical machine, exper'anents 

with. 

. 270 

Electrical sportsman.... 

. 275 

Electrio current, direction of; 

JHW 

ascertained. . , 

. :t > v 




































































IffDEJt. 


455 


Electrical tellurium. 272 i 

Electric tiuid, velocity of . . . . 43 

Electricity.17, 18, 258 

Electricity acquired by induction 278 
Electricity and magnetism, resem¬ 
blance between.302 

Electricitv, animal.282 

“ by induction .... 206 

“ circuit of.265 

Electricity as excited by galvan- . 
ism and by friction, difference 

between.283 

Electricity by transfer.266 

Electricity, effects of similar 

states . 263 

Electricity, frictional . . . 282,283 

Electricity, frictional and chemi¬ 
cal, how they differ.294 

Electricity, galvanic, quantity of. 295 

“ nature of.259 

Electricity, quantity of excited by 
chemical action .... 284 note 
Electricity, simplest mode of ex¬ 
citing .262 

Electricity, the vitreous or posi¬ 
tive, the resinous or negative . 262 
Electricity, three states of . . . 335 

“ voltaic ..283 

Electrics. 258, 260 

Electric telegraph, history of the 329 

Electro-magnet.317 

Electro-magnet, communication 
of magnetism to steel by means 

of.318 

Electro-magnetic multiplier . . 313 
Electro-magnetism . . 17, 260, 308 
Electo-magnet, the U or horse¬ 
shoe .319 

Electro-magnetism, definition of . 18 
Electro-magnetism, discoveries of 
(Ersted, Faraday, Ampere, Ara- 
go, and Sir 11. Davy . . 308, 309 
Electro-magnetism, facts of . . 309 
Electro-magnetic induction . .312 
Electro-magnetic rotation . 313, 316 

note 

Electro-magnetic telegraph, sig¬ 
nal-key and registering appa¬ 
ratus of the.322 

Electro-magnet of Prof. Henry 
and Dr. Ten Eyck .... 317 

Electro-magnetic telegraph . . 319 
Electro-magnetic telegraph, how 
put into operation ..... 324 
Electro-metallurgy ..... 331 

Electrometer.268 

Electrophorus.269 


Electro-plastic process.331 

Electro plating and gilding . . . 331 

Electroscope. ' ... . 269 

Electrotype process.251 

Elementary substances, enumera¬ 
tion of .20 

Elements, the four.19 

Ellipse.341 

Elocution, Barber’s Grammar of . 180 
“ Empty,” common meaning of . 9S 

Endosmoae.27, 112 

Engineer, how enabled to direct 

his guns.65 

Engine, the fire.154 

“ the steam ....... 196 

Equilibrium.74, 75 

- “ of fluids.110 

Equilibrium of fluids, exemplified 
by means of the siphon . . . 133 
Equilibrium of fluids, now disturb¬ 
ed by waves.131 

Equilibrium of fluids of different 

densities.113 

Equilibrium of mercury, water, 

oil, air, &o .113 

Equinoxes.358 

“ precession of the . . .397 
Equivalent, mechanical .... 58 
Ereet, why objects are seen . . .241 

Erbium. 20 

Escapement-wheel.104 

Essential property, meaning of . 21 
Essential properties of matter . 21 

Eunomia.339 

Evaporation, Dr. Watson’3 exper¬ 
iment .150 

Eye.237 

“ a camera obscura.240 

“ different parts of the . . .237 

Eye-glass.248 

Eye, imperfections of, how caused 242 

“ of what composed.237 

Eyes, two, why they do not cause 

double vision.241 

Exercises for solution.53 

Exhausting syringe.163 

Exosmose . . ..27, 112 

Expansibility .27, 29 

Expansion, how it differs from 

dilatation.2? 

Experiments showing inertia ~f 

air.165 

Extension.21, 23 


F. 

Fahienheit’3 thermometer 


143 

























































INDEX. 


!5o 


Falling bodies, law of.51 

Faraday, announcement of in re¬ 
lation to solar spots and mag¬ 
netic variation.. . 304 

Faraday’s discoveries in electro¬ 
magnetism .308 

Faraday’s electro-magnetic appa¬ 
ratus .313 

Faraday \ nomenclature of elec¬ 
tricity .259 

February, why 29 days every 

fourth year.397 

Feldspar.21 

Fire-alarm, the electrical . . . 330 

Fire, as an element.19 

Fire-engine .154 

Fifth.184 

“ how produced.182 

Figure. 21, 23 

Fishes, how thev swim, rise or 

sink, &g .47 

Fixed pulley, mechanical advan¬ 
tage of.8Y 

Fixed pulley, operation of the . 87 
Flavio de Melfi, inventor of mari¬ 
ner’s compass.306 

Flexibility.27, 31 

Float, how heavy bodies can be 

made to.38 

Float-boards of water-wheels . . 82 

Flora. 339 

Florence, experiment made at on 
impenetrability of water . 22, 109 
Fluid and solid bodies, difference 

between.108 

Fluid, definition of.108 

Fluidity of air.142,165 

“ what constitutes . . . 108 

Fluid pressure, law of.115 

Fluids, aeriform.138 

Fluids, aeriform, expanded and 
compressed without limit . . 139 
Fluids and liquids, how different 109 
Fluids, effects of their peculiar 

gravitation.113 

Fluids, equilit riurn of . . .122,133 

Fluids, downward pressure of, 

how shown.114 

Fluids, gravitation of.110 

‘ how different from liquids 109 
' how they gravitate . . .113 
** lateral pressure of . 114, 116 

117 

Fluids level or equilibrium of .110 
“ mechanical agency of . .138 
Fluids of different densities, grav¬ 
itation of . .... 112 


FJaids, particles of, how arranged 114 
“ pressure of ...... IK 

Fluids, pressure of, according to 

height.. . . . 119, 120 

Fluids, pressure of, on what de¬ 
pendent .;.118 

Fluids, pressure of, to what pro¬ 
portional .115 

Fluids, surface of.110 

Fluids, upward pressure of . 114, 117 
Fluids, why unsusceptible of foiin- 

ation into figures.110 

Fluorine.20 

Fly.143 

Flying of birds, how effected . . 47 

Fly-wheels.*. 1 

Fly-wheels and the dead points ' x f 

cranks.. 11 

Fly-wheel in the steam-engine . *,03 

Focus of concave mirrors . . . 22.4 

Fog and dew, difference between 150 

Fog, how produced.150 

Force ..41 

Forces, at an angle. 5o 

“ effects of . . . . 55 

“ three or more in action . 57 

“ unequal at right angles . 56 

Forcing-pump.153 

Formula?.44 

Fortuna.339 

Fountain, glass and jet ... 159 

Fountain, Hero’s.138 

Fountains, artificial, how con¬ 
structed .137 

Fountains, how formed .... 137 

Fourth.184 

Fowling-pieces, length of ... 63 
Franklin, inventor of lightning- 

rods . ..... 281 

Free heat.187 

Frictional electricity . . . 259, 283 

Friction.90 note, 98 

“ cause of.99 

“ how diminished .... 99 

“ how increased.99 

“ loss of power caused by . 99 

** important uses of . . . 100 
Friction of the beds and banks of 

rivers.130 

Friction, particles of fluids desti¬ 
tute of.108 

Friction-wheels.99 

Fuel, combustion of .... ■ .24 

Fulcrum.70, 71, 72 

“ generally a pin or a rivet 76 
Fulcrum in levers of different 
kinds. 77 























































INI) 123.. 


467 


fulcrum of steelyards.74 

Fulton, Robert.200 

Fundamental law of mechanics . 71 
Fusee of a watch.107 

G. 

Galaxy.383 

Galileo. 100, 143, 337 

Galileo’s experiment at Pisa to 
prove his law of falling bodies 52 
Galileo’s law of falling bodies . 52 
Galvanic action, three elements 

necessary for.285 

Galvanic batteries.287 

“ battery.289 

“ circle.286 

Galvanic circle, effects of, how in¬ 
creased .287 

Galvanic circle, essential parts of 

a.286 

Galvanic circle, simplest, of what 

composed.286 

Galvanic electricity.259 

Galvanic electricity, process for 

obtaining.286 

Galvanic fluid, how excited . . 284 

“ piles . ..287 

Galvanism.17,18, 283 

“ facts explained by , . 296 
Galvano-plastic process .... 331 

Galvanotype.331 

Garments, light-colored why cool 191 

“ linen, why cool . . . 189 
Garments, to what they owe their 

strength ..100 

Garments, woollen, why warm . 189 

Garnet.21 

Gaseous bodies, elasticity of . . 30 

Gaseous bodies, to what degree 

they may be dilated.29 

Gases.139 

Gases, how prevented from rising 

from a fl lid.168 

Gay Lussa^'s experiments on the 

velocity A sound.176 

Gearing .83 

Geology.62 

Georgium Sidas.369 

Gibbous.388 

Glucinum.20 

Gold.20 

Gold, both ductile and malleable 31 

“ divisibility of. 23 

Gold, the most malleable of all 

metals.31 

Glaa\ its brittleness . ... 32 


Glass, the bladder ..159 

“ the fountain and jet . . . 159 

“ the hand.158 

“ the India-rubber .... 159 
Glass, why easily cracked when 

suddenly heated.192 

Glass, why used in mirrors . . . 221 

Governor. 106, 200 

Governor applied to steam-engine 
by James Watt ..... 1U6, 293 
Governor, explanation of the . .106 

“ uses of the.106 

Grain of hammered gold .... 23 
Grand law of nature .... 69 note 

Granite.20 

Gravitation, attraction of . . . 27 
** of fluids . . .110,112 

Gravity.25, 33 

Gravity causes pressure of fluids 
upwards as well as downwards.! 17 
Gravity, centre of ... . 37, 59, 66 
Gravity, effect of on density of air 38 
Gravity, effects of on different 

bodies.41 

Gravity, force of, not affected by 

projection.64 

Gravity, force of on projectiles . 62 
“ “ where greatest 35 

“ how it increases and de¬ 
creases .35 

Gravity, law of terrestrial ... 35 
Gravity, specific . . . 40, 126 note 
Gravity, specific, scales for ascer¬ 
taining .126 

Gravity, specific, standard of . . 123 
“ terrestrial ...... 34 

Great Bear.398 

Green sand. 21 

Gregorian telescope ...... 250 

Gridiron pendulums.103 

Grove’s battery.293 

Gudgeons.8C 

Guericke, Otto.158 

Guinea and feather drop . . . .165 

Gunnery, science of.62 

Gunpowder, force of.63 

Gunpowder, great charges of use¬ 
less and dangerous.63 

Guns, how tested.63 

Guns, short ones, why preferable 63 

Gun, the air.164 

Gymnotus electricus ...... 262 

H. 

Hail, how formed.124,150 

“ how it differs from snow . 12-5 




























































168 


INDEX. 


Hair-spring ..104 

Hall, Captain Basil ...... 140 

Halley’s comet as seen by Sir 

John Herschel.379 

Hand-glass.158 

Handles of tea-pots, &o. why of 

wood.190 

Hare’s calorimotor.297 

Harmony.181 

“ how produced .... 183 
Harmony, sconce of, on what 

founded.182 

Harvest-moon.389 

Heat accompanies all great chang¬ 
es in bodies . 110 

Heat, application of its expansive 
power as a mechanical agent . 193 

Ueat and cold.187 

“ conductors of.189 

“ effects of.188 

“ effects of on bodies . . 185,188 
Ileat, effects of on density of sub¬ 
stances .192 

Heat, effects of on water . . 186,194 

Heat, free.187 

first law of.189 

imperfect conductors of . 190 
its effects on a body . . . 141 
most obvious effects of . . 193 

how propagated.190 

latent ..187 

law of the reflection of . .191 

laws of.185 

nature of . . ..185 

of the sun.188 

Heat produced by electrical ac¬ 
tion .188 

Heat, sources of.187 

Hearing trumpets.178 

Heavenly bodies, motion of the 

when the most rapid.350 

Heavenly bodies, why not seen in 

their true place.232 

Heavens, why bright in the day¬ 
time .218 

Hebe.339 

Height of a building, how esti¬ 
mated .53 

Height to which a body projected 
upward will rise ...... 54 

Heliacal ring.318 

Heliography ..257 

Helix.316 

Henry’s and Dr. Ten Eyck’s eiec- 

Tro-magnet .317 

Hero’s fountain.138 


Herschel sees stars through a 

comet.379 

Herschel, Sir J. F. W.’s illustra¬ 
tion of the size and distance of 

the planets.344 

Herschel, Sir John’s opinion of 
the height of the atmosphere . 38 
Herschel’s telescope and its pow¬ 
er . 251,337 

Heterogeneous.19 

lliero employs Archimedes to de¬ 
tect the adulteration of a crown.127 
Hind’s account of the comet of 

1853.381 

Hipparchus, father of astronomy . 336 

Homogeneous.19 

Hornblende.21 

Horizontal motion doc-j not affect 

that of gravity.65 

Horse-power as appliod to the 
steam-engine, meaning of . . 199 
Horses, how made to draw unequal 

portions of a load.77 

Hrtuse’s printing te’egraph . . . 328 
Human voice, powers of the . . 180 
Humor, the vitreous . . . . 237,259 
“ the aqueous .... 237, 239 

Hunter’s moon.388 

“ screw ........ 95 

Hydraulics .... 17, 18, 108, 128 

Ilydraulic-ram.133 

Hydrodynamics.108,129 

Hydro-electric.334 

Hydrogen.20 

“ gas generator . . . .275 

“ pistol.274 

Hydrometer.128 

Hydrostatic bellows, how con¬ 
structed .119 

Hydrostatic paradox.118 

Hydrostatic press, Bramah’s . . 121 
Hydrostatic pressure, as a me¬ 
chanical power.121 

Hydrostatic pressure, caused by 
height, not by quantity . . .119 

Hydrostatics.17, 18, 108 

Ilygeia.339 

Hygrometer.149,150 

Hyperbola.341 

llypersthene.21 


I. 

Ice formed under a recoiver . 
“ how made to melt rapidly . 


1G9 

191 
































































INDEX. 


459 


lfle, why wrapped in woollen or 

packed in shavings.190 

Toe, why wooden spoons and forks 

are used for.190 

Image from concave mirrors . . 225 
“ “ convex mirrors . . 223 

“ inverted.218 

Impenetrability.21, 22 

Imponderable agents .... 18 

Incidence, angle of.48 

Incident motion.47 

Incident rays.216 

Inclination of earth’s axis, effects 

of.354 

Inclined plane. 90 

“ “ advantage of . . 91 

“ “ application of the 91 

“ “ principle of the . 90 

Incombustible bodies.188 

Indestructibility.21, 23 

India rubber.30 

“ “ balls, elasticity of . 47 

“ « glass.158 

Induction, electricity by . . 266, 278 
“ electro-magnetic . .312 

Inertia. 21, 24, 26, 41 

“ experiment to illustrate . 25 

“ of air. 38, 143, 165 

“ of a fluid, effects of the . 134 

“ of fly-wheels.81 

“ of water.98 

Inferior conjunction.349 

“ planets.343 

Infusoria.23 

Instruments for raising water . .131 
Insulated, meaning of . . . 261, 270 
Intensity as applied to electricity, 

meaning of.295 

“ In vacuo”.98 

^ridiurn. 20 

Iodine.20 

Irene. 339 

Iris of the eye . 237, 238 

Iris, the planet or asteroid . . . 339 

Iron.20 

Iron, a knowledge of the uses of 
the first step towards civiliza¬ 
tion .31 

ton, ductile but not malleable 

into thin plates.31 

i. 9n, how made brittle.30 

“ oxide of.21 

“ when most malleable ... 31 
Tvory, elasticity cf.30,46 


J ansen.SS’S 

Jerusalem, siege of . . . . 106 

Jet, the straight and revolving 163 

Jointed discharger. 261 

Juno.339 

Jupiter. 367,368 

Jupiter, a prolate spheroid, and 

why.62 

Jupiter’s belts .368 

Jupiter, satellites of.367 

K. 

Kaleidoscope.222 

Kepler'.337 

“ laws of . . . . 337,350,352 

Kepler’s opinion of tho number of 

comets.380 

Klinkenfues.381 

Knee-joint.96 

L 

Ladder a lever.. 77 

Lakes, why more difficult to swim 

in.126 

Lamp, defects of, how remedied . 112 

Lamps, why they will not burn . Hi 

Lamp, wick of, how it supplies the 

flame.Ill 

Lantanium.20 

Latent heat..187 

Lathes.i, 80 

Law, Bode’s.342 

Law, fundamental of mechanics, 
pyronomics, acoustics and op¬ 
tics .49 

Law, Mariotte’s.142 

“ of falling bodies.51 

Laws of heat.*185 

“ of reflected sound . . . ..178 
Laws of reflection from concave 

mirrors.. . 226, 227 

Law of the heavenly bodies . . 340 

Lead.20 

“ not ductile.31 

“ why heavy.34 

Le Verrier ...... ... 371 

Leap-year.396 

Leaves of a wheel ... .84 

Length. 23 

Lens, axis of a. 233 





























































460 


INDEX. 


Lens, concavo-convex .... 23a 

convex as a burning-glass . 235 

“ double concave.233 

“ double convex.233 

Lenses . 232 

Lens, effect of how estimated . . 234 
“ focal distance of a . . . .234 

Lenses in spectacles.236 

Lens, single concave.233 

“ single convex.233 

“ the crystalline.237 

Level, how ascertained.113 

“ or equilibrium of fluids . 110 

Levels, spirit or water.113 

Lever.93 

“ advantage in use of . . . 73 
Lever, force of the, on what de¬ 
pendent .76 

Lever, how used.72 

•* kinds of.72 

“ many forms of the .... 75 

“ of first kind.73 

«* of second kind ...... 76 

“ of third kind.78 

“ perpetual, the.80 

Lever, power of not dependent on 

its shape.76 

Lever, principle of the .... 71 

*« the bent.76 

Lever, things to be considered in 

the.72 

Leyden-jar.263 

“ how charged .... 271 
Leyden-jar, how discharged silent¬ 
ly .265 

Light, aberration of.384 

“ absorbed by all bodies . .217 

“ beam ol .213 

“ color of ..... . 251,252 
Light, corpuscular and undulatory 

theories of.211 

Light, heat and chemical action 

o£.254 

Light, how projected.213 

Light, intensity of, law of de¬ 
crease .212 

Light, passing into different medi¬ 
ums .230 

Light, polarization of.256 

“ reflected.215 

“ “ laws of .... 216 

“ reflection of.211 

Light, Sir Isaac Newton’s opinion 

of.211 

Light, theories of.211 

Light, thermal, chomical and non- 
optieai effects of.256 


Light, velocity of. .45 

“ zodiacal.360 

Lightning, how caused.278 

Lightning-rods.265 

“ by whom invented 281 

Lightning-rods, the best, how con¬ 
structed .280 

Lime.21 

Lime, carbonate of.21 

Linen garments, why cool . . . 189 

Line of direction.66 

Liquid, how it differs from a fluid 109 
Liquids have a slight degree of 

cohesion.109 

Liquids not easily compressed . 29 
Liquid, quantity of discharged 

from an orifice.129 

Lithium.20 

Load-stone. 298 

Locomotive steam-engine . . . 208 

Looking-glasses.221 

Looking-glass, length of to reflect 

the whole person.223 

Lucifer.363 

Luminous bodies.210 

Lutetia 339 

M. 

Machino.71 

Machinery, propelled by electrici¬ 
ty .279 

Machine, Attwood’s.52 

Machines, velocity of, how regu¬ 
lated . *..... 106 

Magazine, magnetic.307 

Magdeburgh cups.157 

Magnesia.21 

“ carbonate of .... 21 

Magnesium.20 

Magnet, attraction and repulsion 

of. 300,301 

Magnet, attractive power of, where 

greatest.300 

Magnet, broken.302 

Magnet communicates its prop¬ 
erties .301 

Magnet, dipping of a.303 

“ effect of heat upon . . 302 
Magnet, horse-shoe or U, how 

armed.308 

Magnetic influence, all bodies sus¬ 
ceptible of.301 

Magnetic magazine.307 

Magnetic needle.304 

Magnet, keeper of a . „ . . 302,308 
Magnet, properties of . . . 299 





































































INDEX. 




Magnetic poles .... .300 

“ power oa surface . . . 302 

Magnetism.11 18,208 

Magnetism and electricity, re¬ 
semblances of.. . 302 

Magnet, modes of supporting . . 300 
Magnetic poles, where strongest 304 
Magnet, north and south poles of, 
where most powerful .... 306 
Magneto-electricity .... 1’, 332 
Magneto-electricity, most power¬ 
ful effects of, how obtained . .332 
Magneto-eleetric machine . . . 333 

Magnet, polarity of. 299 

Magnet, poles of changed by elei 

tricity.393 

Magnet, powers of, how increased 301 

“ kinds of.299 

“ artificial, how made.306, 301 

** the receiving.32” 

“ U or horse-shoe . . . . 30 J 

** variation of . 303, 304 note 
Magnitude, centre of ... 59, 66 

Main-spring of a watch . . 104, 107 

Major third .184 

Malleability.27,31 

Malleability dependent on tem- 


perature .... 


Manganese .... 


Marco Paolo . 


Mariner’s compass 


Mariner’s compass, 

inventor of 


the. 306 

Mariner’s compass, needle of, how 

placed . 305 

Mariner’s compass, how mounted 305 
“ “ points of the 305 

Mariotte’s law.142 

Mars.366 

Massiia.339 

Materials, strength of.95 

Materials which compose the crust 

of the earth.20 

Materials, tenacity of.32 

Matter, attractive.34 

“ definition of.19 

“ essential properties of . 21 
“ gaseous form of ... . 19 
Matter, its different states or 

forms.19 

Matter, liquid form of.19 

Matter, quantity of, how estimat¬ 
ed . 40 

Materiality of air.162 

Matter, solid form of.19 

Mechanioal agency of fluids . .118 
“ equivalent.68 


Mechanical operations always at¬ 
tended by heat . 188 

Mechanical paradox.68 

“ power.70 

“ powers.7i 

Mechanical powers, enumeration 

of the.12 

Mechanical powers, on what prin¬ 
ciple constructed.71 

Mechanical powers, principal law 

of the.89 

Mechanical powers, reducible to 

three classes.72 

Mechanical properties of gases, 

vapors, &g .139 

Mechanics.17.41 

‘f fundamental law of. 71, 91 

111’ 

Mechanics, fundamental law of, 
its application to hydrostatic 

pressure . 119 

Media. 97, 22$ 

Medium.97 

Mediums. 97, 229 

Medium in optics.* 23G 

Melpomene.339 

Meniscus .233 

Mercurial pendulum.103 

** tube.160 

Mercury.20 

“ the planet, transit of . . 363 
Mercury, the planet, why not often 

seen.362 

Metallic points.265 

Metals, good conductors of heat . 190 

“ names of the.20 

Metals, order of their conducting 

power of heat.190 

Metals, tenacity cf.32 

Meteoric stones . ..387 

Meteoric stones, J*~. Brewster’s 

opinion of.367 

Metes. 339 

Mica.21 

Microscope, a double.243 

“ a single.242 

Microscope, compound urp-gnify- 
ing power of, how ascertained 244 
Microscope, magnifying power of, 

how ascertained.244 

Microscope, the solar.244 

Microscope, the solar, magnifying 

power of.241 

Microscopes, what have tin 
greatest magnifying power . 24 r 

Milk, why affected by tfiund'' 

and lightning . . . J8’ 
































































462 


INDRX. 


Milky-way.383 

Minor thirl.184 

Mirror.221 

“ concave . ..222 

“ convex ..222 

“ plain.. . 221 

Mirrors of half the he ght show a 
whole-length figure . . . . 217 

Mirrors reverse all images . . 222 

“ use of glass in . . . . 221 

Miscellaneous experiments with 

air.166 

Mobility.27 

Molybdenum.20 

Momenta.50 

Momentum.41,50 

Momentum of a body, how ascer¬ 
tained .50 

Monochord.182 

Moon.386 

. “ as cause of tides.391 

“ as seen through a telescope 389 
Moon, common errors in respect 

to the.386 

Moon, density of the.387 

** difference in daily rising 389 

*« gibbous.388 

** harvest and hunter’s . . 389 

“ horned . 388 

“ in quadrature.388 

Moon-light, objects seen by, why 

faint.217 

Moon, surface of the.386 

“ uninhabitable.364 

Morienne.144 

Morse’s telegraph.320 

“ telegraphic alphabet . . 323 

Motion.41 

Motion, accelerated, retarded and 

uniform.44 

Motion, axis of.59 

“ centre of.59 

Motion, how transmitted by hy¬ 
drostatic pressure . 121 

Motion, incident and reflected . 47 
Motion impelled by two or more 

forces.. . . 55 

Motion of the heavenly bodies, 

cause of the.34 

Motion, perpetual.45 

“ regulators of.1G0 

** reversed.83 

Motion, slow or rapid pro luced at 
pleasure by machinery .... 84 
Motion, when imperceptible . . 220 
Moving power in machines, how 
stopped.85 


Mountain, how burst by hydro¬ 
static pressure.126 

Musical scale.183 

“ sounds . 181 

Multiplier, electro-magnetic . .313 

Multiplying-glass.235 

Musical chord, how produced . . 182 
Musical instruments, why affected 

by the weather.182 

Music of a choir dependent on the 
uniform velocity of sound . .176 
Music of strings, how caused . .181 
Mutual attraction.34 


-N. 

Natural Philosophy, definition of 17 


Neap tides.391 

Needle, the magnetic.304 

Needle, how placed in a mariner’s 

compass.305 

Negative electricity .... 259, 262 
“ (galvanic) pole . . . 287 

Neptune.371 

Newcomen and Savary’s steam- 

engine .197 

Newton, Sir Isaac .... 23, 337 

Newton, Sir Isaac, discovery of 

gravitation.100 

Newton’s discoveries, on what 

based.352 

Newton’s (Sir Isaac) opinion of 

light. . 211 

Newton, Sir Isaac’s, opinion of the 
earth’s compressibility ... 29 

Nickel. 20, 298 

Niobium.20 

Nitrogen. 20 

Non-conductors . . . *158, 260 

Non-electrics. 258, 260 

Nut and screw. . 9$ 


O. 

Oars, on what principle construct 

ed.77 

Object, apparent size of, on what 

dependent . 220 

Objects, when invisible . 218, 220 

Octave. 184 

“ how produced.182 

(Ersted’s discoveries ;n electro 

magnetism . . ..308 

Oil, effects of in smoothing the 

surface of water. 131 

Oil, glutinous matter iu . . ,111 

Oil-mills. 92 


































































INDEX. 


463 


Oil, why it floats.39 

Olber’a, Dr., opinion on lunacy . 386 

Opaque bodies.217 

Opera-glasses.249 

Opposition.350 

Optical paradox .212 

Optic-nerve. 237, 240 

Optics.17, 210 

** definition of ....... 18 


Oracles of Delphi, Ephesus, <fcc. . 180 

Orbit, meaning of.340 

Orbits of the planets, inclination 

of.347 

Orbits of the planets, not circular 343 


Otto Guericke. 


“ Out of beat,” meaning of. 

. .104 

Overshot-wheel. 


Osmium.. 


Oxyde of iron. 


Oxygen . 



P. 


Pails, why two can be carried 


more easily than one . . 

# # 

69 

Palladium. 


20 

Pallas. 


339 

Parabola. 

62, 

341 

Parachute. 


38 

Paradox. 


118 

“ acoustic. 


177 

“ hydrostatic . . . . 


118 

“ mechanical . . . . 


68 

“ optical. 


212 

“ pneumatio . . . . 


169 

Paradox, optical, pneumatic, 

acous- 

tic, &<s. t no paradox . . 

212 note 

Parallax. 


385 

Parallel motion, appendages 

for 

200 

Parallelogram. 


48 

Parthenope .. 


339 

Pascal .. 


144 

Pelopium. 


20 

Pendulum. 


100 

Pendulum, cause of slowness and 


rapidity of vibrations .... 102 
Pendulums, continuous motion 

of, how preserved.103 

Pendulum, how lengthened or 

shortened ..102 

Pendulum, how to be suspended 103 
“ its motion, how caused 101 
Pendulums, length of, proportion 

of.103 

Pondulum, length of to vibrate 
Boconds ... 102 


Pendulum, length of to viorate 

two seconds.103 

Pendulum, length of varies with 

the latitude.102 

Pendulums, table of the lengths 
of to beat seconds in different 

latitudes.104 

Pendulum, the ballistic .... 03 

“ the gridiron .... 103 

“ the mercurial .... 103 

Pendulums, to what variations 

subject..103 

Pendulum, use of the ball of.101 note 

Penumbra.394 

Percussion, force of.93 

Perigee.349 

Perihelion.349 

Permanent magnets.301 

Perpendicular.48 

Perpetual lever.80 

“ motion.45 

Perpetual motion, approximation 

to . . ..288 

Phocea. 339 

Phosphor . 303 

Phosphorus.20 

Photography.257 

Physical spectra.228 

Physics, definition of.17 

Piazzi . 343 

Pincers.75 

Pinions.83 

Pipes, tones of, on what dependent 181 

Pivots.81 

Plane, the inclined.90 

Planet, meaning of.339 

Planet and star, difference be¬ 
tween .339 

Planets, characters by which they 

are represented.346 

Planets, inferior and superior. . 343 

“ minor. 339,307 

“ “ how discovered . 342 

Planets, minor, by whom discov¬ 
ered .. 343 

Planets, minor, size of.344 

“ names of the . . . 338, 339 

Planets, relative appearance of, 
as seen through a telescope . 372 

Planets, the primary.338 

Planets, when in a particular con¬ 
stellation . * ...... . 349 

Platinum.20 

Platinum, both ductile and malle¬ 
able..31,32 

Plough, constellation of the . . 398 

Plumb-line. ,..3" 









































































164 


INDEX. 


Pneumatics.17 18, 138 

Pneumatic balloon.161 

Pneumatic paradox.169 

“ shower-bath .... 166 

“ scales.160 

Pointers.398 

Poker.75 

Polarity.299 

“ boreal and austral . . . 302 

Polarization of light.256 

Polar or pole star. 384, 398 

Poles, magnetic . .... . 300,304 
Poles, magnetic, where strongest 304 

Ponderable agents.18 

Pope Callixtus and the comet of 

Halley.378 

Pores.28 

Porosity . .27,28 

Positive electricity .... 259, 262 
Positive (galvanic) pole .... 287 

Potash.21 

Potassium.20 

Power.72 

Power, how gained by use of the 

lever.76 

Power, how to be understood 73 note 

Powers, mechanical.70, 72 

Power that acts. 7 

Power, weight and velocity, pro¬ 
portion of.90 

Precession of the equinoxes. . . 397 
Press, Bramah’s hydrostatic . .121 
Presses, screws applied to ... 95 
Pressure at any depth, how esti¬ 
mated .115 

Pressure, fluid, law of.115 

Pressure, hydrostatic, as a me¬ 
chanical power.121 

Pressure, hydrostatic, caused by 
height, not by quantity . . .119 

Pressure of fluids.114 

Pressure of fluids in proportion to 

height of column.120 

Pressure of the air .... 141,162 
“ of water at great depths 109 
Pressure on hydrostatic bellows, 

how estimated.119 

Primary planets.338 

Principle of all machines ... 72 
Principle of the mechanical pow¬ 
ers .71 

Prism.252 

Projectiles.62 

Projectile, random of.65 

Projection, force of ..*... 62 
Projection, foreo of, has io effect 
ou gravity.64 


Propeller. 204 

Properties, essentia/ and acciden* 

tai, of matter.21 

Properties, essential and unessen¬ 
tial .23 

Prussian blue. 327 

Psyche.. < 339 

Ptolemy.. . 336 

Pulley.86 

“ fixed and movable ... 86 

“ fixed, use of.87 

Pulleys, mechanical principle of 
same as that of levers .... 88 
Pulley, movable, how it differs 

from a fixed.87 

Pulley, movable, principle of the 89 
Pulley, power of, how ascertained 88 
Pulleys, practical use of ... . 89 

Pump, the chain.131 

“ the common, for water . . 152 

“ the forcing.153 

“ the air.154 

Pupil. 237,238 

Pyramid, why the firmest of struc¬ 
tures .68 

Pyrometer.193 

“ Wedgewood’s . . . 193 

Pyronomics .... 17, 18, 185, 187 
Pythagoras. 336 


Q. 


Quadrature.388 

Quartz.zl 


Questions for solution 36, 42, 43, 50 
53, 54, 78, 86, 90, 96, 106, 116, 127, 

184 


R. 


Radiation of heat..190 

lladii.48 

Radius.48 

“ vector . 350 

Rain, how formed . . . 124,150, 186 
Rainbow, how produced .... 255 

Ram, the battering.105 

“ the hydraulic. 133 

Random of a projectile .... 65 

Rarefaction.140 

Rarefied.140 

Rarity.27, 28 

Ray of light.212 

Rays of light absorbed . . . .215 

| “ “ converging . . . 212 

| Rays, converging and diverging, 

1 laws of. . 227 

































































INDEX" 


t6o 


Rajs of light, diverging . . . *i2 

hays of light from terrestrial ob¬ 
jects .213 

Reader, The Rhetorical .... 180 

Reaumur’s thermometer . . . 149 

Receiver.154 

Rectangle.. 48 

Rectilinear motion converted to 

circular . ..... 81 

Reflected motion.47 

Reflecting substances.211 

“ telescope .... 246,249 

Refraction.229 

Refracting substances.211 

“ telescope.246 

Refrangibility.230 

Registering apparatus of the tel¬ 
egraph . 322 

Regulators of motion.100 

Rein, F. C., hearing trumpets or 

cornets.178 note 

Repulsion.28 

Resinous electricity.262 

Resistance.41 

Resistance of a medium, to what 

proportioned.97 

Resistance of the air .....' 38 

“ to be overcome ... 71 

Resultant.68 

“ motion.57 

** of two forces .... 66 

Resultant of two forces, how de¬ 
scribed .68 

Retarded motion of bodies pro¬ 
jected upwards.54 

Retina. ... 237, 240 

Reversed motion .83 

Revolving-jet.163 

Revolution of the planets, length 

of.341 

Rhetorical Reader.180 

Rhodium.. 20 

Rhodes, siege of .105 

Rifles, how tested.63 

Rivers, how formed.124 

Rivers, why difficult to swim in . 126 

Rivulets, how formed . . . 124, 136 

Roads, inclined planes .... 91 

Rolling friction.98 

Romans, the ancient, how they 

conveyed water.137 

Rope-dancer, how enabled to per¬ 
form his feats.67 

Ropes, strength of, on what de¬ 
pendent .100 

Rosso’s telescope.251 

Rotation, electro-magnetic . .313 


Rudders, on what principle con¬ 
structed . 77 

Rules relating to musical strings 184 
Rules by which changes of* the 
weather may be prognosticated 
by means of the barometer . . 147 
Rules relating to musical pipes . 184 
Rush’s Treatise on the Voice . . 180 
Ruthenium.. 20 


S. 


Safety-valve.199 

Sagacity of animals ...... 92 

Sap, ascent of, to what due .112 
Satellites, general law of . . . .370 

Sat/urn.368 

Saturn’s rings.368 

Scales for ascertaining specific 

gravity.126 

Scale, the musical ....... 183 

Scales, the pneumatic.16C 

Schorl.21 

Science of harmony, on what 

founded .IS 2 

Scissors. 75 

Sclerotica.23 T 

Screw. 93 


“ a compound power .... 94 
“ advantage of the .... 94 
“ convex and concave ... 94 
** power of, how estimated . 94 


“ Hunter’s.95 

“ of Archimedes . . . . . . 132 

“ uses of the. 95 

“Sea-Eagle,” experiment made 

on board of the.109 

Seasons, cause of the.350 


explanation of the cause 355, 
356 


Sea-water, cause of its increased 

specific gravity. 120 

Seebeck, Professor, discoveries of 
in thermo-electricity .... 334 

Selenium.20 

Serpentine.21 

Shadow.213 

Shadows, darkest, how produced 214 
Shadows from several luminous 

bodies.215 

Shadows, increasing and diminish 

ing.214 

Shadow of a spherical body, form 

of.214 

Shadows, why of different degrees 

of darkness.213 

Shaft ....... .81 




































































4G6 


INDEX. 


Shej herds, balancing of in south 

of France.67 

Ships, on what principle they float 123 

Sidereal time.396 

“ year.396 

Silence produced by two sounds 177 

Silica . ^.20, 21 

Silver best conductor of heat . . 19 ' 

Simple motion.55 

Sidereal year, how measured . . 397 
Signal-key of the electrio tele¬ 
graph .322 

Signs of the zodiac.346 

Signs used in almanacs .... 389 

Silurus electricus.282 

Silver.*. . . . 20 

Siphon .132 

Siphon, equilibrium of fluids ex¬ 
emplified by means of the . . 1S3 
Siphon, experiments with the . 167 
“ principle of the .... 133 

Sky, why blue.253 

Slate formations in Bohemia . . 23 
Slaves in West Indies, how they 

steal rum.122 

Steel, how made brittle .... 30 

Sliding friction ..98 

Smee’s battery.290 

Smoke, why it ascends.39 

Snow, how formed .... 124,150 
“ how it differs from hail . 124 
Snow and ice, how made to melt 

rapidly.191 

Smuffers.75 

Soap-bubble, thickest part of . . 23 

Soda.21 

Sodium.20 

Solar microscope.214 

Solar system, account of the 337,338 

“ time.396 

“ year, how measured . 396,397 

Solstices.358 

Sonorous bodies.174 

Sonorous property of bodies, to 

what due.175 

Sound.174 

Sound affected by the furniture 

of a room.179 

Sound, by what laws reflected . . 178 
Sound, by what reflected and dis¬ 
persed .179 

Sound, focus of.179 

Sound, how communicated most 

rapidly .175 

Sour.d of the human voice . . .179 
“ of strings, ho-/ caused . . 181 
“ rapidity of.176 


Sounds, distance to which they 


may be conveyed.176 

Sounds, musical.181 

“ producing silence ... 177 
Sound, velocity of . . . .176 note 
Sounds, what pleasing to the ear 183 

“ when loudest.174 

Sources of heat.187 

Space.41 

“ how estimated.43 

Speaking-trumpets.178 

Specific gravity .... 40, 1 26 note 
Specific gravity of bodies, how as¬ 
certained . 125,127 

Specific gravity, scales for ascer¬ 
taining .126 

Specific gravity, standard of . .123 
“ gravities, table of . . .124 

Sphericity, centre of.37 

Spectacles.236 

Spectrum of a prism.254 

Spherical aberration.247 

Spherical body, how made to roll 
down a slope ........ 68 

Spider’s web.23 

Spiral tube.274 

Spirit level.113 


Spirit or water level, with what 


filled.113 

Spots in the sun.304 

Sportsman aiming at a bird ... 57 
Spring, how high it will rise . . 137 

Springs, how formed.136 

Spring-tides.391 

Spur-gear.84 

Spur-wheel.84 

Square.48 

Square rods, why bi tter than round 
as conductors of electricity . .279 
Standard of specific gravity . .123 

Stars, distance of the.382 

Stars, distance of the, Sir John 
Hcrschel’s opinion of .... 383 
Stars, how distinguished from 

planets.339 

Stars, the fixed.381 

Stars, why not seen in the day¬ 
time .363 

Stars, why not seen in their true 

place.384 

Statics.17,18 

Stationary steam-engine .... 209 

Steam.195 

Steamboats. . . 203 

Steam, cause of the ascent of . .124 
“ dry and invisible .... 196 
Steam engino applied to boats . 203 
































































INDEX. 


467 


S'.eam-er.gine, power of, how esti- \ 

mated.199 

Steam-engine, the.196 

“ improvers of the . 290 

Steam-engine, Newcomen and Sa- 

vary’s . 197 

Steaui-engine, Watts’ double act¬ 
ing, condensing.197 

S.eam-engine, Watts’ improve¬ 
ments of the.197 

Steam-engine, the locomotive 294, 

208 

Steam-engine, the stationary . . 209 
Steam-engine, Tufts’ stationary 207 
Steam, foundation of its applica¬ 
tion to machinery.30 

Steam, how condensed into water 195 
“ how made to act .... 196 

Steam, on what its mechanical 
agency depends ....... 195 

Steam, pressure of, on what de¬ 
pendent .195 

Steam-ship.203 

Steam, space occupied by . . . 196 

“ temperature of.195 

“ why it ascends.39 

Steatite . . . ..21 

Steelyards.75 

“ how to be used . . 74 
Steelyards, mechanical principle 

of the.73 

Stereo-electric current.334 

Stethoscope.175 

Still.194 

Stilts used in south of France . 67 

Straight jet.163 

Strata of the earth.20 

Stream, velocity of, how measured 130 
Strings, musical sounds of, how 

produced.181 

Strings, musical quality of the 

sounds of ..181 

Strontium.20 

Struve’s opinion of the distance 

of the stars. 382 

Substance, heterogeneous ... 19 
“ homogeneous .... 19 

Sucker.160 

Sulphate of copper battery . . . 292 
Sulphate of copper battery (pro¬ 
tected) .293 

Sulphur.20 

Sun, as cause of tides ..... 391 
“ as viewed from the planets 360 

“ its size, Ac.359 

linn, uioon and plauets, relative 
size of the ..343 


Sun, planets and stars, inhabited 359 
Sun, red appearance of the, how 


caused.253 

Sun’s heat, effect of on the earth. 150 

Superior conjunction.349 

“ planets.343 

Surinam eel. 282 

Suspension of action.85 


Synchronous tickings of a clock . 104 
Syracuse, King of, employs Ar¬ 
chimedes to detect the adultera¬ 
tion of a crown ..... 127 note 
Syringes for striking fire . . . .188 
Syringe, the condensing . . 156,163 


T. 


Table of specific gravities . . . 124 
Table of the lengths of pendulums 104 


“ of velocities.42 

Tackle and fall.89 

Talc.21 

Tangent.48,60 

Tantalus.. 133 note 

Tantalus’ cup.133 

Tantalize, origin of the word . .133 

Tapestry of Bayeux.380 

Tea-pots, why they have handles 

of wood.190 

Teeth.83 

Telegraph, atmospheric . , . .331 
“ Bain’s.326 


“ electric, history of the 329 

“ electro-magnetic . . 319 

Telegraph, electro-magnetic, rep¬ 


resentation of the.323 

Telegraph, electric, principles of 

its construction.320 

Telegraph, House’s printing . 328 

Telegraphic battery.321 

Telegraph, meaning of . .319 note 

Telescopes.246 

Telescope, achromatic.247 

“ Cassegrainian ... 250 

“ day and night . . . 248 

** Gregorian.250 

“ Herschel’s.251 

“ “ power of .337 

“ Lord Rosse’s .... 251 

“ reflecting.246 

“ refracting.246 

“ simplest form of the . 247 

Tellurium.20 

Tenacity. 27,32 

“ of cords.32 

“ of the metals , . . . . 32 


of metals, how increased 3? 

























































468 


INDEX. 


Tenacity of various substances . 32 
Tender of a steam-engine . . . 204 

^erbium.. 20 

Terrestrial gravity.34 

L'hermal etfects of light .... 256 

Thermometer.. . 149 

“ Celsius’.149 

“ Delisle’s.149 

** Fahrenheit’s . . . 149 

Thermometer, on what principle 

constructed.29 

Thermometer, Reaumur’s . . . 149 

Thermo-electric.334 

** batteries.... 335 

Thermo-electricity . . . . 260,334 

Thetis.339 

Thorium.20 

Threads of a screw.93 

Thunder-clouds, distance of, how 

measured.177 

Thunder-house.277 

Thunder-storm, safest position in.281 

Tides.390 

“ neap and spring.391 

Time, apparent and true, differ¬ 
ence between.397 

Time as kept by clock and by the 

sun.397 

Time employed in the ascent and 
descent of a body equal ... 54 

Time, how estimated.43 

“ sidereal and solar .... 396 
Time of ascent and descent of a 

body.45 

Tin.20 

Tin and copper, sonorous proper¬ 
ties of.30 

Tin, not ductile.31 

Tissue figure. 270 

Titanium.20 

Toggle-joint .. 96 

“ operation of the . . 97 
Tones of the voice, how varied . 180 

Tonic.183 

Tonnage of vessels, how estimated 123 

Torpedo . 282 

Torricelli.143 

Torricellian vacuum.143 

Towns and fortifications, attacks 

on.63 

Transfer of fluids.167 

Transit of Mercury and Venus . 363 
Translucent bodies . . .... 211 

Transparent bodies.211 

Tropic . ..356 

Trumpet.178 

Trumpets, hearing.178 


Trumpet, speaking ... .178 

Tubes, capillary ..... .111 

“ mercurial ..... .160 

Tufts’ stationary steam-engine . 207 

Tune ..41 

Tungsten.20 

Tycho Drahe. 336 


U. 


Umbrella, use of in leaping from 

high places. 

Undershot wheel. 

Undulations of light. 

“ of water, effects of . 
Undulatory theory of light . . . 

Universal discharger. 

Urania.. 

Uranium. 

Uranus ..t . 

“ moons of. 

Ursa Major. 


38 

8 q 

211 

131 

211 

272 

339 

20 

369 

370 
398 


V. 


Vacuum.98, 143 

Vacuum, a perfect, not to be pro¬ 
cured by means of the air-pump 156 
Vacuum, the Torricellian . . . 143 

Valve . . s .152 

Vanadium.20 

Vapor, cause of ascent of . . . .124 

Vapors.139 

Vegetables, why white or yellow 
when growing in dark places . 256 
Vehicle in motion, cause of acci¬ 
dents from.25 

Velocities, table of.42 

Velocity.41,71 

“ absolute and relative . . 42 

“ how estimated.42 

Velocity of balls thrown by gun¬ 
powder ..63 

Velocity of light and of the elec¬ 
tric fluid.40 

Velocity of parts of a body, how 

diminished.60 

Velocity of sound . . .176 and note 
Velocity of sound, distances 

measured by the.177 

Velocity of sound, experiments of 
Arago, Gay Lussac and others 17C 
Velocity of a stream how meas¬ 
ured .130 

Velocity of the surface of a 
stream, greatest .... . 129 































































INDEX. 


409 


Velocity required in machines. 


how regulated.106 

Ventriloquism.180 

Venus ..303 

“ transit of.363 

Venus, why never seen late at 

night.363 

Vertical line.37 

Vesicular form of matter, defi¬ 
nition of.19 

Vespasian, battering-ram of . .106 

Vesper.363 

Vessels, tonnage of, how esti¬ 
mated .123 

Vesta.331) 

Vision, angle of.219 

Victoria.339 

Vitreous electricity.262 

Vitreous humor. 237,239 

Vitriol, effects of on water . . . 187 

Voice, I)r. Rush’s Treatise on the 180 

“ sound of the.179 

Voice, the human, imitative pow¬ 
er of the.180 

Voice, tones of the, how varied . 180 

Voltaic battery.289 

“ electricity . . . 259,283 

'« pile.288 


W. 


?Var, how it has been elevated to 

a science. 63 

Warmth of clothing, cause of . . 189 
Watch, how it differs from a clock. 104 

“ how regulated.105 

“ moving power of a . . . 104 

Water.21 

Water, converted into steam, space 

occupied by.30 

Water, distilled, the standard of 

specific gravity.123 

Water, elasticity and compressi¬ 


bility of.*. . 24 

Water expands when freezing . . 192 
Water-fowl, buoyancy of . . . .123 
Water frozen under the air-pump. 169 
Water, how applied to move ma¬ 
chinery .83 

Water, how converted into steam.195 
Water, how high raised by means 

of common pump.153 

Water, how much diminished in 

bulk by pressure.29 

Water, instruments for raising . 131 

Water-level.113 

VVater, motion of, how retarded . 129 

40 


Water, not destitute of compress¬ 
ibility . 109 

Water, of what composed . . 20 

Water, pressure of at great 

depths.109,116 

Water, pressure of at any depth, 

how estimated.115 

Water, pressure of at different 

depths.115 

Water-pump.152 

Water-spouts. 172 

Water, weight of a cubic foot of . 126 
“ weight of a cubic inch of 115 
Water when falling, why less in¬ 
jurious than ice.114 

Water, when perfectly pure . . 124 
Water, why it appears more shal¬ 
low than it is.. . 231 

Water-wheels.81 


“ most powerful . . 82 
Watson, Dr., experiment of, to 
show degree of evaporation . . 150 

Watt, James.106 

Watt, James, his improvements 

of the steam-engine.197 

Waves, how caused.130 

Waves of light, laws of . .212 note 

Wedge.92 

“ advantage of the .... 92 
Wedge, effective power of, on 

what dependent.92 

Wedge, power of the.92 

Wedges, use of.92 

Wedgewood’s pyrometer . . . .193 

Weight.34, 72 

“ cause of.34 

“ lifter. 165 

Weight, loss of in bodies weighed 

in water.126 

Weight of any body, how ascer¬ 
tained by its cubical contents . 125 
Weight raised by wheel and axle, 

how supported.79 

Weight, what bodies have the 

greatest.34 

Welding ..31 

Wheel and axle.78 

“ “ advantage of . 79 

** “ construction of . 79 

“ “ how supported . 81 

“ “ principle of the . 80 

Wheel, escapement.104 

Wheels, friction.99 

Wheels in machinery acting as 

levers.78 

Wheels, large and small, advan¬ 
tages of each ... .... 85 
























































470 


INDEX. 


Wheels, locked, how and woj . 85 
Wheels of a clock, their use 101 

“ power of.. 80 

“ size of limited by wbat 85 

“ tires of how secured . 193 

Wheels, toothed, method ot ascci 

taining power of.85 

Wheels, use of on roads .... 85 
Wheol with teeth, of three kinds 84 

Whirlwinds.. . .172 

Whispering-gallery.1/9 

Whispering-gallery in Newbury- 

port.179 

Whisper, motion of a, rapidity of 

the.176 

White.251 

• Whitefield.179 

Wick of a lamp, principle of the 111 
Width.23 


Wightman’s apparatus for inertia 25 
William, Duke of Normandy . .380 
William the Conqueror .... 380 
Winch applied to wheel and axle 79 

“ double. 80 

Wind. ... 170 

Wind, cause of the different direc¬ 
tions of the.171 

Wind, east, cause of at the equa¬ 
tor .171 

Wind instruments, sound of, on 

what lependent.181 

Winds quality of the, how affect¬ 
ed .... «... 171 


Wind, why it subsides at sunset . 17i 


Windlass. . . . .83 

Windlass and capstan, difference 

between..80 

Wind-mills.80 

Window, where the hand should 

be applied to raise.77 

Wollaston, experiments of . . . 254 

Wooden spoons and forks, why 

preferred for ice.190 

Woollen garments, why warm . 189 

Worcester, Marquis of ... 200 
Worm of a still.195 

Y. 

Year. 341 

Year, leap.396 

Year, sidereal and solar . . . 396 

Yttrium.20 

Z 

Zodiac.345 

Zodiacal light . . ^.360 

Zodiac, constellations of the, 

change of.347 

Zodiac, signs oi the.346 

Zinc.20 

Zinc, at what temperature malle¬ 
able . . ..81 

Ziroonium ....... . 2£ 


































































































































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